Catalytic dehydration of hydroxypropionic acid and its derivatives

ABSTRACT

Hydroxypropionic acid, hydroxypropionic acid derivatives, or mixtures thereof are dehydrated using a catalyst and a method to produce bio-acrylic acid, acrylic acid derivatives, or mixtures thereof. A method to produce the dehydration catalyst is also provided.

FIELD OF THE INVENTION

The present invention generally relates to methods for catalyticdehydration of hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof to acrylic acid, acrylic acid derivatives, ormixtures thereof with high yield and selectivity to acrylic acid,acrylic acid derivatives, or mixtures thereof, short residence time, andwithout significant conversion of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof to undesired sideproducts, such as, for example, acetaldehyde, propionic acid, aceticacid, 2,3-pentanedione, carbon dioxide, and carbon monoxide.

BACKGROUND OF THE INVENTION

Acrylic acid, acrylic acid derivatives, or mixtures thereof have avariety of industrial uses, typically consumed in the form of polymers.In turn, these polymers are commonly used in the manufacture of, amongother things, adhesives, binders, coatings, paints, polishes,detergents, flocculants, dispersants, thixotropic agents, sequestrants,and superabsorbent polymers (SAP), which are used in disposableabsorbent articles, comprising diapers and hygienic products, forexample. Acrylic acid is commonly made from petroleum sources. Forexample, acrylic acid has long been prepared by catalytic oxidation ofpropylene. These and other methods of making acrylic acid from petroleumsources are described in the Kirk-Othmer Encyclopedia of ChemicalTechnology, Vol. 1, pgs. 342-369 (5^(th) Ed., John Wiley & Sons, Inc.,2004). As petrochemical resources become increasingly scarce, moreexpensive, and subject to regulations for CO₂ emissions, there exists agrowing need for bio-based acrylic acid, acrylic acid derivatives, ormixtures thereof that can serve as an alternative to petroleum-basedacrylic acid, acrylic acid derivatives, or mixtures thereof.

Many attempts have been made over the last 80 years to make bio-basedacrylic acid, acrylic acid derivatives, or mixtures thereof fromnon-petroleum sources, such as lactic acid (also known as2-hydroxypropionic acid), lactic acid derivatives (e.g. alkyl2-acetoxy-propionate and 2-acetoxy propionic acid), 3-hydroxypropionicacid, glycerin, carbon monoxide and ethylene oxide, carbon dioxide andethylene, and crotonic acid. From these non-petroleum sources, onlylactic acid is produced today in high yield from sugar (≥90% oftheoretical yield, or equivalently, ≥0.9 g of lactic acid per g ofsugar). Furthermore, commercial lactic acid purity and economics couldfavor producing acrylic acid at a cost competitive to petroleum-basedacrylic acid. As such, lactic acid or lactate presents a realopportunity of serving as a feedstock for bio-based acrylic acid,acrylic acid derivatives, or mixtures thereof. Also, 3-hydroxypropionicacid is expected to be produced at commercial scale in a few years, andas such, 3-hydropropionic acid will present another real opportunity ofserving as feedstock for bio-based acrylic acid, acrylic acidderivatives, or mixtures thereof. Sulfate salts, phosphate salts,mixtures of sulfate and phosphate salts, bases, zeolites or modifiedzeolites, metal oxides or modified metal oxides, and supercritical waterare the main catalysts which have been used to dehydrate lactic acid orlactate to acrylic acid, acrylic acid derivatives, or mixtures thereofin the past with varying success.

For example, U.S. Pat. No. 4,786,756 (issued in 1988), describes thevapor phase dehydration of lactic acid or ammonium lactate to acrylicacid using aluminum phosphate (AlPO₄) treated with an aqueous inorganicbase as a catalyst. As an example, the '756 patent discloses a maximumyield of acrylic acid of 43.3% when lactic acid was fed into the reactorat approximately atmospheric pressure, and a respective yield of 61.1%when ammonium lactate was fed into the reactor. In both examples,acetaldehyde was produced at yields of 34.7% and 11.9%, respectively,and other side products were also present in large quantities, such aspropionic acid, CO, and CO₂. Omission of the base treatment causedincreased amounts of the side products. Another example is Hong et al.,Appl. Catal. A: General 396:194-200 (2011), who developed and testedcomposite catalysts made with Ca₃(PO₄)₂ and Ca₂(P₂O₇) salts with aslurry-mixing method. The catalyst with the highest yield of acrylicacid from methyl lactate was the 50%-50% (by weight) catalyst. Ityielded 68% acrylic acid, about 5% methyl acrylate, and about 14%acetaldehyde at 390° C. The same catalyst achieved 54% yield of acrylicacid, 14% yield of acetaldehyde, and 14% yield of propionic acid fromlactic acid.

Prof. D. Miller's group at Michigan State University (MSU) publishedmany papers on the dehydration of lactic acid or lactic acid esters toacrylic acid and 2,3-pentanedione, such as Gunter et al., J. Catalysis148:252-260 (1994); and Tam et al., Ind. Eng. Chem. Res. 38:3873-3877(1999). The best acrylic acid yields reported by the group were about33% when lactic acid was dehydrated at 350° C. over low surface area andpore volume silica impregnated with NaOH. In the same experiment, theacetaldehyde yield was 14.7% and the propionic acid yield was 4.1%.Examples of other catalysts tested by the group were Na₂SO₄, NaCl,Na₃PO₄, NaNO₃, Na₂SiO₃, Na₄P₂O₇, NaH₂PO₄, Na₂HPO₄, Na₂HAsO₄, NaC₃H₅O₃,NaOH, CsCl, Cs₂SO₄, KOH, CsOH, and LiOH. In all cases, the abovereferenced catalysts were tested in gas phase reactions with low partialpressures of water, as commonly suggested in the art for dehydrationreactions. Finally, the group suggested that the acrylic acid yield isincreased (and the by-product yields are decreased) when the surfacearea of the silica support is low, the reaction temperature is high, thereaction pressure is low, and the residence time of the reactants in thecatalyst bed is short.

Finally, the Chinese patent application 200910054519.7 discloses the useof ZSM-5 molecular sieves modified with aqueous alkali (such as NH₃,NaOH, and Na₂CO₃) or a phosphoric acid salt (such as NaH₂PO₄, Na₂HPO₄,LiH₂PO₄, LaPO₄, etc.). The best yield of acrylic acid achieved in thedehydration of lactic acid was 83.9%, however that yield came at verylong residence times.

Therefore, the manufacture of acrylic acid, acrylic acid derivatives, ormixtures thereof from lactic acid or lactate by processes, such as thosedescribed in the literature noted above, has demonstrated: 1) yields ofacrylic acid, acrylic acid derivatives, or mixtures thereof notexceeding 70% at short residence times; 2) low selectivities of acrylicacid, acrylic acid derivatives, or mixtures thereof, i.e., significantamounts of undesired side products, such as acetaldehyde,2,3-pentanedione, propionic acid, CO, and CO₂; 3) long residence timesin the catalyst beds; and 4) catalyst deactivation in short time onstream (TOS). The side products can deposit onto the catalyst resultingin fouling, and premature and rapid deactivation of the catalyst.Further, once deposited, these side products can catalyze otherundesired reactions. Aside from depositing on the catalysts, these sideproducts, even when present in only small amounts, impose additionalcosts in processing acrylic acid (when present in the reaction producteffluent) towards the manufacture of SAP, for example. Thesedeficiencies of the prior art processes and catalysts render themcommercially non-viable.

Accordingly, there is a need for catalysts, methods of making thecatalysts, and processes for the dehydration of hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof to acrylic acid,acrylic acid derivatives, or mixtures thereof, with high yield andselectivity toward acrylic acid, in an efficient manner (i.e. shortresidence times), and with suitable catalyst longevity.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a method for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The method comprises contacting: (a) hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; (b) water vapor;and (c) a dehydration catalyst comprising one or more amorphousphosphate salts; wherein said one or more amorphous phosphate saltsconsist essentially of: i) one or more monovalent cations, and ii) oneor more phosphate anions selected from the group represented byempirical formula (I):[H_(2(1−x))PO_((4−x))]⁻  (I);

wherein x is any real number equal to or greater than 0 and equal to orless than 1; wherein said one or more amorphous phosphate salts in saiddehydration catalyst are neutrally charged;

wherein the water partial pressure during said contacting step is equalto or greater than the water partial pressure at the triple point ofsaid one or more amorphous phosphate salts; wherein said contacting stepis performed at a temperature equal to or greater than the temperatureat the triple point of said one or more amorphous phosphate salts; andwhereby said acrylic acid, acrylic acid derivatives, or mixtures thereofis produced as a result of said water vapor and said hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof beingcontacted with said dehydration catalyst.

In one embodiment of the present invention, a method for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The method comprises contacting:

(a) a gas mixture comprising: i) hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof; and ii) water vapor; with

(b) a dehydration catalyst comprising one or more amorphous phosphatesalts; wherein said one or more amorphous phosphate salts consistessentially of: i) one or more monovalent cations, and ii) one or morephosphate anions selected from the group represented by empiricalformula (I):[H_(2(1−x))PO_((4−x))]⁻  (I);

wherein x is any real number equal to or greater than 0 and equal to orless than 1; wherein said one or more amorphous phosphate salts in saiddehydration catalyst are neutrally charged;

wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than the water partial pressure atthe triple point of said one or more amorphous phosphate salts; whereinsaid contacting step is performed at a temperature equal to or greaterthan the temperature at the triple point of said one or more amorphousphosphate salts; and whereby said acrylic acid, acrylic acidderivatives, or mixtures thereof is produced as a result of said watervapor and said hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof being contacted with said dehydration catalyst.

In one embodiment of the present invention, a method for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The method comprises contacting:

(a) a gas mixture comprising: i) hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof; and ii) water vapor; with

(b) a dehydration catalyst comprising one or more amorphous phosphatesalts; wherein said one or more amorphous phosphate salts consistessentially of: i) one or more monovalent cations, and ii) one or morephosphate anions selected from the group represented by empiricalformula (I):[H_(2(1−x))PO_((4−x))]⁻  (I);

wherein x is any real number equal to or greater than 0 and equal to orless than 1; wherein said one or more amorphous phosphate salts in saiddehydration catalyst are neutrally charged;

wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than about 4 bar; wherein saidcontacting step is performed at a temperature equal to or greater thanabout 250° C.; and whereby said acrylic acid, acrylic acid derivatives,or mixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst.

In one embodiment of the present invention, a method for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The method comprises contacting:

(a) a gas mixture comprising: i) hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof; and ii) water vapor; with

(b) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts; wherein said one or more precursor phosphatesalts consist essentially of: i) one or more monovalent cations, and ii)one or more phosphate anions selected from the group represented bymolecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer number equal to or greater than 1; wherein z isany integer number equal to or greater than 3; wherein said one or moreprecursor phosphate salts are neutrally charged;

wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than the water partial pressure atthe triple point of said one or more precursor phosphate salts; whereinsaid contacting step is performed at a temperature equal to or greaterthan the temperature at the triple point of said one or more precursorphosphate salts; and whereby said acrylic acid, acrylic acidderivatives, or mixtures thereof is produced as a result of said watervapor and said hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof being contacted with said dehydration catalystprecursor mixture.

In one embodiment of the present invention, a method for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The method comprises contacting:

(a) a gas mixture comprising: i) hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof; and ii) water vapor; with

(b) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts; wherein said one or more precursor phosphatesalts consist essentially of: i) one or more monovalent cations, and ii)one or more phosphate anions selected from the group represented bymolecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer number equal to or greater than 1; wherein z isany integer number equal to or greater than 3; wherein said one or moreprecursor phosphate salts are neutrally charged;

wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than about 4 bar; wherein saidcontacting step is performed at a temperature equal to or greater thanabout 250° C.; and whereby said acrylic acid, acrylic acid derivatives,or mixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst precursormixture.

In one embodiment of the present invention, a method for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The method comprises contacting: (a) a gas mixturecomprising: i) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; and ii) water vapor; with (b) a dehydrationcatalyst precursor mixture consisting essentially of: (KPO₃)_(n) andSiO₂; wherein the water partial pressure during said contacting step insaid gas mixture is equal to or greater than about 4 bar; wherein saidcontacting step is performed at a temperature equal to or greater thanabout 250° C.; and whereby said acrylic acid, acrylic acid derivatives,or mixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst precursormixture.

In one embodiment of the present invention, a method for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The method comprises contacting:

(a) a gas stream comprising: i) lactic acid, ii) water, and iii)nitrogen; wherein said lactic acid is present in an amount of about 2.5mol %, wherein said water is present in an amount of about 50 mol %based on the total moles of said gas stream; with

(b) a dehydration catalyst precursor mixture consisting essentially of(KPO₃)_(n) and SiO₂ in a weight ratio between about 1:1 and about 1:7;

wherein said contacting step of said gas stream with said dehydrationcatalyst precursor mixture is performed at a temperature from about 325°C. to about 400° C., at a WHSV between about 0.25 (g of lactic acid/g ofcatalyst·h) and about 1.0 (g of lactic acid/g of catalyst·h), and at atotal pressure between about 10 barg and about 25 barg, in a reactorhaving an interior surface material selected from the group consistingof amorphous silica and borosilicate glass; whereby acrylic acid isproduced as a result of said water and said lactic acid being contactedwith said dehydration catalyst precursor mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure, reference should bemade to the following detailed description and drawing Figures.

FIG. 1 illustrates the calculation of amorphous content in thedehydration catalyst using an XRD technique. The separate amorphous(I_(A)) and crystalline (I_(C)) contributions to the scattering patternare determined using a profile-fitting technique, after appropriatebackground subtraction.

FIG. 2 illustrates a typical water partial pressure versus temperaturephase equilibrium diagram of a dehydration catalyst (amorphous phosphatesalt) and its precursor phosphate salts (crystalline phosphate salts).The triple point is located in the interception of the three phaseboundary curves. M^(I) is a monovalent cation. The reported values ofwater partial pressure are only an illustration and do not represent thereal values for every specific dehydration catalyst described in thecurrent invention.

While the disclosed catalysts and methods are susceptible of embodimentsin various forms, there are illustrated in the figures (and willhereafter be described) specific embodiments of the invention, with theunderstanding that the disclosure is intended to be illustrative, and isnot intended to limit the invention to the specific embodimentsdescribed and illustrated herein.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

As used herein, the term “bio-based” material refers to a renewablematerial.

As used herein, the term “renewable material” refers to a material thatis produced from a renewable resource.

As used herein, the term “renewable resource” refers to a resource thatis produced via a natural process at a rate comparable to its rate ofconsumption (e.g., within a 100 year time frame). The resource can bereplenished naturally, or via agricultural techniques. Non-limitingexamples of renewable resources include plants (e.g., sugar cane, beets,corn, potatoes, citrus fruit, woody plants, lignocellulose,hemicellulose, and cellulosic waste), animals, fish, bacteria, fungi,and forestry products. These resources can be naturally occurring,hybrids, or genetically engineered organisms. Natural resources, such ascrude oil, coal, natural gas, and peat, which take longer than 100 yearsto form, are not considered renewable resources. Because at least partof the material of the invention is derived from a renewable resource,which can sequester carbon dioxide, use of the material can reduceglobal warming potential and fossil fuel consumption.

As used herein, the term “petroleum-based” material refers to a materialthat is produced from fossil material, such as petroleum, natural gas,coal, etc.

As used herein, the term “catalyst” refers to either a pre-reactioncatalyst (also called a catalyst precursor mixture) or an in-situcatalyst. The pre-reaction catalyst is the catalyst loaded into thechemical reactor, and the in-situ catalyst is the catalyst present inthe reactor during the reaction. In general, a catalyst increases thereaction rate without being consumed in the reaction. Finally, apre-reaction catalyst can remain unchanged during the reaction orundergo in-situ physical or chemical transformations during the reactionthat can change its physical and chemical properties and become anin-situ catalyst.

As used herein, the term “monophosphate” or “orthophosphate” refers toany salt whose anionic entity, [PO₄]³⁻, is composed of four oxygen atomsarranged in an almost regular tetrahedral array about a centralphosphorus atom.

As used herein, the term “condensed phosphate” refers to any saltscontaining one or several P—O—P bonds generated by corner sharing of PO₄tetrahedra.

As used herein, the term “polyphosphate” refers to any condensedphosphates with a linear structure; i.e. containing linear P—O—Plinkages by corner sharing of PO₄ tetrahedra leading to the formation offinite chains.

As used herein, the term “cyclophosphate” refers to any condensedphosphate with a cyclic structure.

As used herein, the term “hydrated” refers to a hydrated crystallinesalt or hydrated crystalline compound that contains a specific number ofwater molecules per formula unit of the salt or compound.

As used herein, the term “monovalent cation” refers to any cation with apositive charge of +1.

As used herein, the term “polyvalent cation” refers to any cation with apositive charge equal or greater than +2.

As used herein, the term “anion” refers to any atom or group ofcovalently-bonded atoms having a negative charge.

As used herein, the term “heteropolyanion” refers to any anion withcovalently bonded XO_(p) and YO_(r) polyhedra, and thus comprises X—O—Yand possibly X—O—X and Y—O—Y bonds, wherein X and Y represent any atoms,and wherein p and r are any positive integers.

As used herein, the term “heteropolyphosphate” refers to anyheteropolyanion, wherein X represents phosphorus (P) and Y representsany other atom.

As used herein, the term “phosphate adduct” refers to any compound withone or more phosphate anions and one or more non-phosphate anions thatare not covalently linked.

As used herein, the term “amorphous” refers to the state of anycondensed phase material that lacks the long-range order characteristicof a crystalline material. An amorphous material can be either anamorphous solid or a liquid. In the context of the present invention,materials with more than 50 wt % of amorphous content are consideredamorphous materials.

As used herein, the term “crystalline” refers to the state of anycondensed phase material whose constituents are arranged in a highlyordered microscopic structure, forming a crystal lattice with long-rangeorder. In the context of the present invention, materials with less than50 wt % of amorphous content are considered crystalline materials.

As used herein, the term “chemically inert” materials refers tomaterials which remain in the same chemical form, under equilibriumconditions, when contacted with another material or materials. In thecontext of the present invention, more than about 90 wt % of thematerial should remain in the same chemical form to be considered a“substantially chemically inert” material and more than about 98 wt % ofthe material should remain in the same chemical form to be considered an“essentially chemically inert” material.

As used herein, the term “antioxidant” refers to a molecule capable ofterminating radical chain processes by either donating a hydrogen atomor the reaction of an olefinic bond to form a stabilized organic radicaland thus terminate radical chain processes. Non limiting examples ofantioxidants comprise thiols, polyphenols, butylated hydroxy toluene(BHA), and butylated hydroxy anisole (BHA).

As used herein, the terms “LA” refers to lactic acid, “AA” refers toacrylic acid, “AcH” refers to acetaldehyde, “PA” refers to propionicacid, “LAC” refers to LA conversion in mol %, “AAY” refers to AA yieldin mol %, “AAS” refers to AA selectivity in mol %, “PAS” refers to PAselectivity in mol %, “AcHY” refers to acetaldehyde yield in mol %, and“23PDY” refers to 2,3-pentanedione yield in mol %.

As used herein, the terms “LA” refers to lactic acid, “AA” refers toacrylic acid, “AcH” refers to acetaldehyde, and “PA” refers to propionicacid.

As used herein, the term “conversion” in % is defined as[hydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof flow rate in (mol/min)−hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof flow rate out(mol/min)]/[hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof flow rate in (mol/min)]×100. For the purposes of thisinvention, the term “conversion” means molar conversion, unlessotherwise noted.

As used herein, the term “yield” in % is defined as [product flow rateout (mol/min)/hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof flow rate in (mol/min)]×100. For the purposes ofthis invention, the term “yield” means molar yield, unless otherwisenoted.

As used herein, the term “selectivity” in % is defined as[Yield/Conversion]×100. For the purposes of this invention, the term“selectivity” means molar selectivity, unless otherwise noted.

As used herein, the term “total carbon balance” is defined as: [((molcarbon monoxide out+mol carbon dioxide out+mol methane out)+(2×(molacetic acid out+mol acetaldehyde out+mol ethane out+mol ethyleneout))+(3×(mol acrylic acid out+mol propionic acid out+molhydroxypropionic acid out+mol hydroxyacetone out)+(5×mol 2,3pentanedione out)+(6×mol acrylic acid dimer out))/(3×molhydroxypropionic acid in)]×100. If hydroxypropionic acid derivative isused instead of hydroxypropionic acid, the above formula needs to beadjusted according to the number of carbon atoms in the hydroxypropionicacid derivative.

As used herein, the term “Gas Hourly Space Velocity” or “GHSV” in h⁻¹ isdefined as 60×[Total gas flow rate (mL/min)/catalyst empty bed volume(mL)]. The total gas flow rate is calculated under Standard Temperatureand Pressure conditions (STP; 0° C. and 1 atm).

As used herein, the term “Weight Hourly Space Velocity” or “WHSV” in h⁻¹is defined as 60×[Total LA flow rate (g/min)/catalyst weight (g)].

As used herein, the term “Liquid Hourly Space Velocity” or “LHSV” in h⁻¹is defined as 60×[Total liquid flow rate (mL/min)/catalyst bed volume(mL)].

II. Catalysts for the Conversion of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives

Unexpectedly, it has been found that catalysts comprising a mixture ofpartially dehydrated dihydrogen monophosphates of monovalent cations inthe amorphous state can dehydrate hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof to acrylic acid,acrylic acid derivatives, or mixtures thereof with high: 1) yield andselectivity for acrylic acid, acrylic acid derivatives, or mixturesthereof, i.e., low amount and few side products; 2) efficiency, i.e.,performance in short residence time; and 3) longevity. As a non limitingexample, these amorphous phosphate salts can be formed reversibly whencrystalline phosphate salts (e.g. monophosphates, polyphosphates, orcyclophosphates) of monovalent cations with molar ratio of phosphorus tocations of about 1 are contacted with water at elevated water partialpressure and temperature. The applicants also found unexpectedly, thatin order to dehydrate hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof to acrylic acid, acrylic acidderivatives, or mixtures thereof, the dehydration catalyst of thepresent invention needs to be in the presence of sufficient water vapor,contrary to common belief in the art of performing dehydration reactionsunder dry conditions. Although not wishing to be bound by any theory,applicants hypothesize that the water vapor is required to avoid fulldehydration of the dihydrogen monophosphate salts to condensedphosphates under operation conditions, maintaining the Brønsted acidsites that are required for the selective acid-catalyzed dehydration ofhydroxypropionic acid and its derivatives to acrylic acid and itsderivatives.

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts; wherein said one ormore amorphous phosphate salts consist essentially of: (a) one or morecations, and (b) one or more phosphate anions selected from the grouprepresented by empirical formula (I):[H_(2(1−x))PO_((4−x))]⁻  (I);

wherein x is any real number equal to or greater than 0 and equal to orless than 1; and wherein said one or more amorphous phosphate salts ofsaid dehydration catalyst are neutrally charged. In another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsconsisting essentially of: (a) one or more cations, and (b) one or morephosphate anions selected from the group represented by empiricalformula (I); wherein x is any real number equal to or greater than 0 andequal to or less than 1 such that the salt is crystalline; wherein saidone or more crystalline phosphate salts of said dehydration catalyst areneutrally charged. In another embodiment of the present invention, saidone or more cations are selected from the group consisting of monovalentcations, polyvalent cations, and mixtures thereof. In yet anotherembodiment of the present invention, said one or more cations areselected from the group consisting of monovalent cations.

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts; wherein said one ormore amorphous phosphate salts consist essentially of: (a) one or moremonovalent cations, and (b) one or more phosphate anions selected fromthe group represented by empirical formula (I):[H_(2(1−x))PO_((4−x))]⁻  (I);

wherein x is any real number equal to or greater than 0 and equal to orless than 1; wherein said one or more amorphous phosphate salts of saiddehydration catalyst are neutrally charged. In another embodiment of thepresent invention, at least one of said one or more amorphous phosphatesalts is replaced by one or more crystalline phosphate salts consistingessentially of: (a) one or more monovalent cations, and (b) one or morephosphate anions selected from the group represented by empiricalformula (I); wherein x is any real number equal to or greater than 0 andequal to or less than 1; wherein said one or more crystalline phosphatesalts of said dehydration catalyst are neutrally charged.

The amorphous phosphate salts that comprise one or more phosphate anionsrepresented by empirical formula (I) can be a mixture of amorphousmonophosphates and polyphosphates of different length (e.g. M^(I)H₂PO₄,M^(I) ₂H₂P₂O₇, M^(I) ₃H₂P₃O₁₀, M^(I) ₄H₂P₄O₁₃, . . . M^(I)_(n)H₂P_(n)O_((3n+1)); wherein M^(I) is a monovalent cation). As a nonlimiting example, this mixture can be produced by partial dehydration ofdihydrogen monophosphates or by partial hydrolysis of condensedphosphates with molar ratio of phosphorus to cations of about 1. Theamorphous phosphate salts can also comprise any hydrated form of saidmonophosphates and polyphosphates. In the context of the presentinvention, the variable x in empirical formula (I) refers either to thecomposition of single species within said mixture of monophosphates andpolyphosphates or to the average composition of said mixture.

In the context of the present invention, a phosphate salt or a mixtureof phosphate salts with more than 50 wt % of amorphous content (or lessthan 50 wt % of crystalline content) are considered amorphous phosphatesalts. The amorphous content can be determined by any method known tothose skilled in the art, such as, by way of example and not limitation,x-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy,differential scanning calorimetry (DSC), or solid-state nuclear magneticresonance (NMR) spectroscopy. As an illustration, in a method based onan XRD technique (see FIG. 1), the separate crystalline (I_(C)) andamorphous (I_(A)) contributions on the X-ray scattering pattern aredetermined using a profile-fitting technique. This deconvolution of thescattering pattern into the separate contributions can be performedusing Gaussian, Lorentzian, Voigt, or related functions known to thoseskilled in the art. Then, the amorphous content, X_(A), is determined bycalculating the ratio between the area of scattered intensity for theamorphous contribution (I_(A)) and the area of the total scatteredintensity (crystalline plus amorphous contributions, I_(T)=I_(C)+I_(A))for a defined Bragg angle range (e.g. 2θ=5° to 50°, Cu-radiationλ=1.54059 Å, in the context of the current invention), i.e.

$X_{A} = {\frac{I_{A}}{I_{C} + I_{A}} \times 100\mspace{14mu}{wt}\mspace{14mu}{\%.}}$

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts represented by empiricalformula (Ia):M^(I)H_(2(1−x))PO_((4−x))  (Ia);

wherein M^(I) is a monovalent cation; wherein x is any real number equalto or greater than 0 and equal to or less than 1. In another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsrepresented by empirical formula (Ia); wherein M^(I) is a monovalentcation; wherein x is any real number equal to or greater than 0 andequal to or less than 1.

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts represented by empiricalformula (Ib):M_(w) ^(I)N_((1−w)) ^(I)H_(2(1−x))PO_((4−x))  (Ib);wherein M^(I) and N^(I) are two different monovalent cations; wherein xis any real number equal to or greater than 0 and equal to or less than1; wherein w is any real number greater than 0 and less than 1. Inanother embodiment of the present invention, at least one of said one ormore amorphous phosphate salts is replaced by one or more crystallinephosphate salts represented by empirical formula (Ib); wherein M^(I) andN^(I) are two different monovalent cations; wherein x is any real numberequal to or greater than 0 and equal to or less than 1; wherein w is anyreal number greater than 0 and less than 1.

In the context of the present invention, “one or more cations” refers todifferent types of cations and “one or more anions” refers to differenttypes of anions. Non limiting examples of cations are metallic cations,organo-metallic cations, ammonium, substituted ammonium, oxycations, andother cations known by those skilled in the art. Non limiting examplesof substituted ammonium and other cations are isopropylammonium,ethylenediammonium, sarcosinium, L-histidinium, glycinium, and4-aminopyridinium. Non limiting examples of oxycations are pervanadyland vanadyl ions.

Non limiting examples of monovalent cations of said one or moreamorphous phosphate salts are cations of alkali metals, organo-metalliccations, ammonium, substituted ammonium, oxycations (e.g. pervanadyl),and other cations known by those skilled in the art. In one embodimentof the present invention, said one or more monovalent cations of saidone or more amorphous phosphate salts are selected from the groupconsisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, and mixtures thereof. Inanother embodiment of the present invention, said one or more monovalentcations of said one or more amorphous phosphate salts are selected fromthe group consisting of Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof. In yetanother embodiment of the present invention, said one or more monovalentcations of said one or more amorphous phosphate salts is K⁺.

In another embodiment of the present invention, at least one of said oneor more amorphous phosphate salts consists of two or more differentmonovalent cations selected from the group consisting of Li⁺, Na⁺, K⁺,Rb⁺, Cs⁺, Ag⁺, and Tl⁺. In another embodiment of the present invention,at least one of said one or more amorphous phosphate salts consists oftwo or more different monovalent cations selected from the groupconsisting of Na⁺, K⁺, Rb⁺, and Cs⁺.

In one embodiment of the present invention, the amorphous phosphatesalts are selected from the group consisting of LiH_(2(1−x))PO_((4−x)),NaH_(2(1−x))PO_((4−x)), KH_(2(1−x))PO_((4−x)), RbH_(2(1−x))PO_((4−x)),CsH_(2(1−x))PO_((4−x)), any of their hydrated forms, and mixturesthereof; wherein x is any real number equal to or greater than 0 andequal to or less than 1. In another embodiment of the present invention,the amorphous phosphate salt is KH_(2(1−x))PO_((4−x)); wherein x is anyreal number equal to or greater than 0 and equal to or less than 1.

In one embodiment of the present invention, the amorphous phosphatesalts are selected from the group consisting ofLi_(w)Na_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Cs_((1−x))H_(2(1−x))PO_((4−x)),K_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrated forms, andmixtures thereof; wherein x is any real number equal to or greater than0 and equal to or less than 1; and wherein w is any real number greaterthan 0 and less than 1.

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts consistingessentially of: i) one or more cations, and ii) one or more phosphateanions selected from the group represented by empirical formula (I):[H_(2(1−x))PO_((4−x))]⁻  (I);

wherein x is any real number equal to or greater than 0 and equal to orless than 1; and wherein said one or more amorphous phosphate salts ofsaid dehydration catalyst are neutrally charged; and (b) one or morenon-phosphate compounds; wherein said one or more non-phosphatecompounds are substantially chemically inert to said one or moreamorphous phosphate salts. In another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts consistingessentially of: i) one or more cations, and ii) one or more phosphateanions selected from the group represented by empirical formula (I);wherein x is any real number equal to or greater than 0 and equal to orless than 1; wherein said one or more crystalline phosphate salts ofsaid dehydration catalyst are neutrally charged. In another embodimentof the present invention, said one or more cations are selected from thegroup consisting of monovalent cations, polyvalent cations, and mixturesthereof. In yet another embodiment of the present invention, said one ormore cations are selected from the group consisting of monovalentcations.

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts consistingessentially of: i) one or more monovalent cations, and ii) one or morephosphate anions selected from the group represented by empiricalformula (I):[H_(2(1−x))PO_((4−x))]⁻  (I);

wherein x is any real number equal to or greater than 0 and equal to orless than 1; and wherein said one or more amorphous phosphate salts ofsaid dehydration catalyst are neutrally charged; and (b) one or morenon-phosphate compounds; wherein said one or more non-phosphatecompounds are substantially chemically inert to said one or moreamorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are essentiallychemically inert to said one or more amorphous phosphate salts. Inanother embodiment of the present invention, said one or morenon-phosphate compounds are chemically inert to said one or moreamorphous phosphate salts. In yet another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts consistingessentially of: i) one or more monovalent cations, and ii) one or morephosphate anions selected from the group represented by empiricalformula (I); wherein x is any real number equal to or greater than 0 andequal to or less than 1 such that the salt is crystalline; wherein saidone or more crystalline phosphate salts of said dehydration catalyst areneutrally charged.

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts represented byempirical formula (Ia):M^(I)H_(2(1−x))PO_((4−x))  (Ia);wherein M^(I) is a monovalent cation; wherein x is any real number equalto or greater than 0 and equal to or less than 1; and (b) one or morenon-phosphate compounds; wherein said one or more non-phosphatecompounds are substantially chemically inert to said one or moreamorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are essentiallychemically inert to said one or more amorphous phosphate salts. Inanother embodiment of the present invention, said one or morenon-phosphate compounds are chemically inert to said one or moreamorphous phosphate salts. In yet another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts represented byempirical formula (Ia); wherein M^(I) is a monovalent cation; wherein xis any real number equal to or greater than 0 and equal to or less than1.

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts represented byempirical formula (Ib):M_(w) ^(I)N_((1−w)) ^(I)H_(2(1−x))PO_((4−x))  (Ib);wherein M^(I) and N^(I) are two different monovalent cations; wherein xis any real number equal to or greater than 0 and equal to or less than1; wherein w is any real number greater than 0 and less than 1; and (b)one or more non-phosphate compounds; wherein said one or morenon-phosphate compounds are substantially chemically inert to said oneor more amorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are essentiallychemically inert to said one or more amorphous phosphate salts. Inanother embodiment of the present invention, said one or morenon-phosphate compounds are chemically inert to said one or moreamorphous phosphate salts. In yet another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts represented byempirical formula (Ib); wherein M^(I) and N^(I) are two differentmonovalent cations; wherein x is any real number equal to or greaterthan 0 and equal to or less than 1; wherein w is any real number greaterthan 0 and less than 1.

In another embodiment of the present invention, the weight ratio betweenthe total amount of said one or more amorphous phosphate salts and thetotal amount of said one or more non-phosphate compounds is betweenabout 1:10 and about 4:1.

In one embodiment of the present invention, said one or morenon-phosphate compounds comprises silicon oxide (SiO₂). In anotherembodiment of the present invention, said one or more non-phosphatecompounds consists essentially of silicon oxide (SiO₂). In anotherembodiment of the present invention, said silicon oxide is selected fromthe group consisting of amorphous silica, quartz, tridymite,cristobalite, moganite, coesite, and mixtures thereof. In anotherembodiment of the present invention, said silicon oxide is amorphoussilica. In yet another embodiment of the present invention, said siliconoxide has a specific surface area of less than about 10 m²/g.

In another embodiment of the present invention, said one or moreamorphous phosphate salts are selected from the group consisting ofLiH_(2(1−x))PO_((4−x)), NaH_(2(1−x))PO_((4−x)), KH_(2(1−x))PO_((4−x)),RbH_(2(1−x))PO_((4−x)), CsH_(2(1−x))PO_((4−x)), any of their hydratedforms, and mixtures thereof, wherein x is any real number equal to orgreater than 0 and equal to or less than 1; and said one or morenon-phosphate compounds are selected from the group consisting ofamorphous silica, quartz, and mixtures thereof. In another embodiment ofthe present invention, said one or more amorphous phosphate salts isKH_(2(1−x))PO_((4−x)), wherein x is any real number equal to or greaterthan 0 and equal to or less than 1; and said one or more non-phosphatecompounds is amorphous silica.

In another embodiment of the present invention, said one or moreamorphous phosphate salts are selected from the group consisting ofLi_(w)Na_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Rb_((1−x))H_(2(1−x))PO_((4−x)),Na_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrated forms, andmixtures thereof; wherein x is any real number equal to or greater than0 and equal to or less than 1; wherein w is any real number greater than0 and less than 1; and said one or more non-phosphate compounds areselected from the group consisting of amorphous silica, quartz, andmixtures thereof.

In one embodiment of the present invention, said one or morenon-phosphate compounds comprise one or more oxysalts comprising: (a)one or more polyvalent cations, and (b) one or more oxyanions selectedfrom the group represented by molecular formulae (II) and (III):[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−)  (II)[Ta_(2d)O_((5d+e))]^(2e−)  (III);wherein a and b are positive integers or zero; wherein c, d, and e arepositive integers; wherein (a−2b) is equal to or greater than zero;wherein (2c−a) is greater than zero; wherein said one or more oxysaltsare neutrally charged. In another embodiment of the present invention,said one or more non-phosphate compounds further comprise silicon oxide(SiO₂).

In another embodiment of the present invention, said one or morenon-phosphate compounds comprise one or more oxysalts comprising: (a)one or more polyvalent cations, (b) one or more monovalent cations, and(c) one or more oxyanions selected from the group represented bymolecular formulae (II) and (III):[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−)  (II)[Ta_(2d)O_((5d+e))]^(2e−)  (III);wherein a and b are positive integers or zero; wherein c, d, and e arepositive integers; wherein (a−2b) is equal to or greater than zero;wherein (2c−a) is greater than zero; wherein said one or more oxysaltsare neutrally charged. In another embodiment of the present invention,said one or more non-phosphate compounds further comprise silicon oxide(SiO₂).

Non limiting examples of said one or more polyvalent cations of said oneor more oxysalts are cations of alkaline earth metals, transitionmetals, post-transition or poor metals, and metalloids; organo-metalliccations, substituted ammonium cations, oxycations (e.g. vanadyl), andother cations known by those skilled in the art. In one embodiment ofthe present invention, said one or more polyvalent cations of said oneor more oxysalts are selected from the group consisting of the cationsof the metals Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W, Mn, Re, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, Bi, La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof. In anotherembodiment of the present invention, said one or more polyvalent cationsof said one or more oxysalts are selected from the group consisting ofthe cations of the metals Mg, Ca, Sr, Ba, Y, Mn, Al, Er, and mixturesthereof. In another embodiment of the present invention, said one ormore polyvalent cations of said one or more oxysalts are selected fromthe group consisting of divalent cations, trivalent cations, tetravalentcations, pentavalent cations, and mixtures thereof. In anotherembodiment of the present invention, said one or more polyvalent cationsof said one or more oxysalts are selected from the group consisting ofBe²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Sc³⁺, Y³⁺, Ti³⁺, Ti⁴⁺, Zr²⁺, Zr⁴⁺, Hf⁴⁺,V³⁺, V⁴⁺, Nb³⁺, Cr²⁺, Cr³⁺, Mo³⁺, Mo⁴⁺, Mn²⁺, Mn³⁺, Re⁴⁺, Al³⁺, Ga³⁺,In³⁺, Si⁴⁺, Ge⁴⁺, Sn⁴⁺, Pb⁴⁺, Sb³⁺, Sb⁵⁺, Bi³⁺, La³⁺, Ce³⁺, Ce⁴⁺, Pr³⁺,Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺, andmixtures thereof. In another embodiment of the present invention, saidone or more polyvalent cations of said one or more oxysalts are selectedfrom the group consisting of Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Y³⁺, Mn²⁺, Mn³⁺,Al³⁺, Er³⁺, and mixtures thereof. In yet another embodiment of thepresent invention, said one or more polyvalent cations of said one ormore oxysalts is Ba²⁺.

Non limiting examples of said one or more monovalent cations of said oneor more oxysalts are cations of alkali metals. In one embodiment of thepresent invention, said one or more monovalent cations of said one ormore oxysalts are selected from the group consisting of the cations ofthe metals Li, Na, K, Rb, Cs, Ag, Tl, and mixtures thereof; and said oneor more polyvalent cations of said one or more oxysalts are selectedfrom the group consisting of the cations of the metals Be, Mg, Ca, Sr,Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Al, Ga, In, Tl, Si,Ge, Sn, Pb, Sb, Bi, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,Lu, and mixtures thereof. In another embodiment of the presentinvention, said one or more monovalent cations of said one or moreoxysalts are selected from the group consisting of the cations of themetals K, Rb, Cs, and mixtures thereof; and said one or more polyvalentcations of said one or more oxysalts are selected from the groupconsisting of the cations of the metals Mg, Ca, Sr, Ba, Y, Mn, Al, Er,and mixtures thereof.

In another embodiment of the present invention, said one or moreoxyanions of said one or more oxysalts are selected from the grouprepresented by molecular formulae (IIa) to (IId), (IIIa) to (IIIg), andmixtures thereof:[SO₄]²⁻  (IIa)[S₂O₇]²⁻  (IIb)[HSO₄]¹⁻  (IIc)[SO₄]²⁻.[HSO₄]⁻  (IId)[Ta₂O₆]²⁻  (IIIa)[Ta₂O₇]⁴⁻  (IIIb)[Ta₂O₉]⁸⁻  (IIIc)[Ta₂O₁₀]¹⁰⁻  (IIId)[Ta₂O₁₁]¹²⁻  (IIIe)[Ta₄O₁₁]²⁻  (IIIf)[Ta₄O₁₅]¹⁰⁻  (IIIg).

In another embodiment of the present invention, said one or moreoxyanions of said one or more oxysalts are selected from the grouprepresented by molecular formulae (IIa), (IIIa), and mixtures thereof:[SO₄]²⁻  (IIa)[Ta₂O₆]²⁻  (IIIa).

Non limiting examples of said one or more oxysalts are sulfates ofalkaline-earth metals, tantalates of alkaline-earth metals, sulfates ofmixed alkali and alkaline earth metals, and tantalates of mixed alkaliand alkaline earth metals. In one embodiment of the present invention,said one or more oxysalts are selected from the group consisting ofCaSO₄, SrSO₄, BaSO₄, SrK₂(SO₄)₂, SrRb₂(SO₄)₂, Ca₂K₂(SO₄)₃, Ca₂Rb₂(SO₄)₃,Ca₂Cs₂(SO₄)₃, CaTa₄O₁₁, SrTa₄O₁₁, BaTa₄O₁₁, MgTa₂O₆, CaTa₂O₆, SrTa₂O₆,BaTa₂O₆, Mg₂Ta₂O₇, Ca₂Ta₂O₇, Sr₂Ta₂O₇, SrK₂Ta₂O₇, Ba₂Ta₂O₇, Ba₃Ta₂O₈,Mg₄Ta₂O₉, Ca₄Ta₂O₉, Sr₄Ta₂O₉, Ba₄Ta₂O₉, Ca₅Ta₂O₁₀, Ca₂KTa₃O₁₀,Ca₂RbTa₃O₁₀, Ca₂CsTa₃O₁₀, Sr₂KTa₃O₁₀, Sr₂RbTa₃O₁₀, Sr₂CsTa₃O₁₀,Mg₅Ta₄O₁₅, Sr₅Ta₄O₁₅, Ba₅Ta₄O₁₅, Sr₂KTa₅O₁₅, Ba₂KTa₅O₁₅, Sr₆Ta₂O₁₁,Ba₆Ta₂O₁₁, any of their hydrated forms, and mixtures thereof. In anotherembodiment of the present invention, said one or more oxysalts areselected from the group consisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆,BaSO₄, BaTa₂O₆, any of their hydrated forms, and mixtures thereof. Inyet another embodiment of the present invention, said one or moreoxysalts are selected from the group consisting of BaSO₄, BaTa₂O₆, anyof their hydrated forms, and mixtures thereof.

In another embodiment of the present invention, said one or moreamorphous phosphate salts are selected from the group consisting ofKH_(2(1−x))PO_((4−x)), RbH_(2(1−x))PO_((4−x)), CsH_(2(1−x))PO_((4−x)),any of their hydrated forms, and mixtures thereof; wherein x is any realnumber equal to or greater than 0 and equal to or less than 1; and saidone or more non-phosphate compounds are selected from the groupconsisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any oftheir hydrated forms, and mixtures thereof. In another embodiment of thepresent invention, said one or more amorphous phosphate salts isKH_(2(1−x))PO_((4−x)), wherein x is any real number equal to or greaterthan 0 and equal to or less than 1; and said one or more non-phosphatecompounds is BaSO₄.

In another embodiment of the present invention, said one or moreamorphous phosphate salts are selected from the group consisting ofK_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrated forms, andmixtures thereof; wherein x is any real number equal to or greater than0 and equal to or less than 1; wherein w is any real number greater than0 and less than 1; and said one or more non-phosphate compounds areselected from the group consisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆,BaSO₄, BaTa₂O₆, any of their hydrated forms, and mixtures thereof.

The variable x in formulae (I), (Ia), and (Ib) is any real number equalto or greater than 0 and equal to or less than 1. In one embodiment ofthe present invention, x is equal to about 0. In another embodiment ofthe present invention, x is equal to about 1. In another embodiment ofthe present invention, x is less than about 0.8. In another embodimentof the present invention, x is less than about 0.6. In anotherembodiment of the present invention, x is less than about 0.5. Inanother embodiment of the present invention, x is between about 0.1 andabout 0.5. In another embodiment of the present invention, x is betweenabout 0.25 and about 0.45. In another embodiment of the presentinvention, x is equal to about 0.4. In yet another embodiment, x isequal to about 0.4 and said one or more monovalent cations is Cs⁺. Thevariable w in formula (Ib) is any real number greater than 0 and lessthan 1. In one embodiment of the present invention, w is less than about0.2 or greater than about 0.8. In another embodiment of the presentinvention, w is less than about 0.1 or greater than about 0.9.

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts; wherein said one ormore amorphous phosphate salts consist essentially of: (a) one or moremonovalent cations, and (b) the phosphate anion represented by molecularformula (Ic):[H₂PO₄]⁻  (Ic);

wherein said one or more amorphous phosphate salts of said dehydrationcatalyst are neutrally charged. In another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts consistingessentially of: (a) one or more monovalent cations, and (b) thephosphate anion represented by molecular formula (Ic).

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts represented by molecularformula (Id):M^(I)H₂PO₄  (Id);

wherein M^(I) is a monovalent cation. In another embodiment of thepresent invention, at least one of said one or more amorphous phosphatesalts is replaced by one or more crystalline phosphate salts representedby molecular formula (Id).

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts represented by molecularformula (Ie):M_(w) ^(I)N_((1−w)) ^(I)H₂PO₄  (Ie);

wherein M^(I) and N^(I) are two different monovalent cations; wherein wis any real number greater than 0 and less than 1. In another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsrepresented by molecular formula (Ie).

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts; wherein said one ormore amorphous phosphate salts consist essentially of: (a) one or moremonovalent cations, and (b) the phosphate anion represented by empiricalformula (If):[PO₃]⁻  (If);

wherein said one or more amorphous phosphate salts of said dehydrationcatalyst are neutrally charged. In another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts consistingessentially of: (a) one or more monovalent cations, and (b) thephosphate anion represented by empirical formula (If). In the context ofthe present invention, the anion represented by empirical formula (If)can refer either to the anion of cyclophosphate salts or to the anion oflong-chain linear polyphosphate salts as described in “Phosphoric Acidsand Phosphates, Kirk-Othmer Encyclopedia of Chemical Technology” byDavid R. Gard (published online: 15 Jul. 2005) and “Phosphorus:Chemistry, Biochemistrty and Technology” by D. E. C. Corbridge (2013).When the empirical formula (If) refers to the anion of long chainpolyphosphate salts, the empirical formula is not precise in that itdoes not include the minor perturbation of excess negative charge owingto the two end-group oxygens.

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts represented by empiricalformula (Ig):M^(I)PO₃  (Ig);

wherein M^(I) is a monovalent cation. In another embodiment of thepresent invention, at least one of said one or more amorphous phosphatesalts is replaced by one or more crystalline phosphate salts representedby empirical formula (Ig).

In one embodiment of the present invention, the dehydration catalystcomprises one or more amorphous phosphate salts represented by empiricalformula (Ih):M_(w) ^(I)N_((1−w)) ^(I)PO₃  (Ih);

wherein M^(I) and N^(I) are two different monovalent cations; wherein wis any real number greater than 0 and less than 1. In another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsrepresented by empirical formula (Ih). In the context of the presentinvention, the salts represented by empirical formula (Ig) or (Ih) canrefer either to cyclophosphate salts or to long-chain linearpolyphosphate salts as described in “Phosphoric Acids and Phosphates,Kirk-Othmer Encyclopedia of Chemical Technology” by David R. Gard(published online: 15 Jul. 2005) and “Phosphorus: Chemistry,Biochemistrty and Technology” by D. E. C. Corbridge (2013). When thesalts represented by empirical formulas (Ig) or (Ih) refer to long chainpolyphosphate salts, the empirical formulae are not precise in that theydo not include the minor amount of either protons or excess monovalentcations needed to produce a charge neutral structure owing to the twoend group oxygens.

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts consistingessentially of: i) one or more monovalent cations, and ii) the phosphateanion represented by molecular formula (Ic):[H₂PO₄]⁻  (Ic);

wherein said one or more amorphous phosphate salts of said dehydrationcatalyst are neutrally charged; and (b) one or more non-phosphatecompounds; wherein said one or more non-phosphate compounds aresubstantially chemically inert to said one or more amorphous phosphatesalts. In another embodiment of the present invention, said one or morenon-phosphate compounds are essentially chemically inert to said one ormore amorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are chemically inertto said one or more amorphous phosphate salts. In yet another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsconsisting essentially of: i) one or more monovalent cations, and ii)the phosphate anion represented by molecular formula (Ic).

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts represented bymolecular formula (Id):M^(I)H₂PO₄  (Id);

wherein M^(I) is a monovalent cation; and (b) one or more non-phosphatecompounds; wherein said one or more non-phosphate compounds aresubstantially chemically inert to said one or more amorphous phosphatesalts. In another embodiment of the present invention, said one or morenon-phosphate compounds are essentially chemically inert to said one ormore amorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are chemically inertto said one or more amorphous phosphate salts. In yet another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsrepresented by molecular formula (Id).

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts represented bymolecular formula (Ie):M_(w) ^(I)N_((1−w)) ^(I)H₂PO₄  (Ie);wherein M^(I) and N^(I) are two different monovalent cations; wherein wis any real number greater than 0 and less than 1; and (b) one or morenon-phosphate compounds; wherein said one or more non-phosphatecompounds are substantially chemically inert to said one or moreamorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are essentiallychemically inert to said one or more amorphous phosphate salts. Inanother embodiment of the present invention, said one or morenon-phosphate compounds are chemically inert to said one or moreamorphous phosphate salts. In yet another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts represented bymolecular formula (Ie).

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts consistingessentially of: i) one or more monovalent cations, and ii) the phosphateanion represented by empirical formula (If):[PO₃]⁻  (If);

wherein said one or more amorphous phosphate salts of said dehydrationcatalyst are neutrally charged; and (b) one or more non-phosphatecompounds; wherein said one or more non-phosphate compounds aresubstantially chemically inert to said one or more amorphous phosphatesalts. In another embodiment of the present invention, said one or morenon-phosphate compounds are essentially chemically inert to said one ormore amorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are chemically inertto said one or more amorphous phosphate salts. In yet another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsconsisting essentially of: i) one or more monovalent cations, and ii)the phosphate anion represented by empirical formula (If).

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts represented byempirical formula (Ig):M^(I)PO₃  (Ig);

wherein M^(I) is a monovalent cation; and (b) one or more non-phosphatecompounds; wherein said one or more non-phosphate compounds aresubstantially chemically inert to said one or more amorphous phosphatesalts. In another embodiment of the present invention, said one or morenon-phosphate compounds are essentially chemically inert to said one ormore amorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are chemically inertto said one or more amorphous phosphate salts. In yet another embodimentof the present invention, at least one of said one or more amorphousphosphate salts is replaced by one or more crystalline phosphate saltsrepresented by empirical formula (Ig).

In one embodiment of the present invention, the dehydration catalystcomprises: (a) one or more amorphous phosphate salts represented byempirical formula (Ih):M_(w) ^(I)N_((1−w)) ^(I)PO₃  (Ih);

wherein M^(I) and N^(I) are two different monovalent cations; wherein wis any real number greater than 0 and less than 1; and (b) one or morenon-phosphate compounds; wherein said one or more non-phosphatecompounds are substantially chemically inert to said one or moreamorphous phosphate salts. In another embodiment of the presentinvention, said one or more non-phosphate compounds are essentiallychemically inert to said one or more amorphous phosphate salts. Inanother embodiment of the present invention, said one or morenon-phosphate compounds are chemically inert to said one or moreamorphous phosphate salts. In yet another embodiment of the presentinvention, at least one of said one or more amorphous phosphate salts isreplaced by one or more crystalline phosphate salts represented byempirical formula (Ih).

In one embodiment of the present invention, at least one of said one ormore amorphous phosphate salts of said dehydration catalyst is ahydrated salt. In another embodiment of the present invention, at leastone of said one or more crystalline phosphate salts of said dehydrationcatalyst is a hydrated salt. In another embodiment of the presentinvention, at least one of said one or more oxysalts of said dehydrationcatalyst is a hydrated salt. In another embodiment of the presentinvention, at least one of said one or more non-phosphate compounds ofsaid dehydration catalyst is a hydrated compound. A hydrated salt orcompound contains a specific number of water molecules per formula unitof the salt or compound. Non limiting examples of hydrated salts orcompounds are hemihydrated, monohydrated, sesquihydrated, dehydrated,trihydrated, tetrahydrated, pentahydrated, hexahydrated, heptahydrated,octahydrated, nonahydrated, nonahydrated, and decahydrated salts orcompounds.

In one embodiment of the present invention, said one or morenon-phosphate compounds of said dehydration catalyst comprises one ormore inert supports. In another embodiment of the present invention,said one or more non-phosphate compounds of said dehydration catalystconsists essentially of one or more inert supports. Non limitingexamples of inert supports are silica or silicates, alumina oraluminates, aluminosilicates, titania or titanates, zirconia orzirconates, carbons (such as activated carbon, diamond, graphite, orfullerenes), sulfates, phosphates, tantalates, ceria, other metaloxides, and mixtures thereof. In the context of the reactions expresslydescribed herein, in one embodiment of the present invention, the inertsupport consists essentially of silicon oxide (SiO₂). In anotherembodiment of the present invention, said silicon oxide is selected fromthe group consisting of amorphous silica, quartz, tridymite,cristobalite, moganite, coesite, and mixtures thereof. In anotherembodiment of the present invention, said silicon oxide is amorphoussilica. In another embodiment of the present invention, said siliconoxide has a specific surface area of less than about 10 m²/g. Whenpresent, the inert support represents an amount of about 20 wt % toabout 90 wt %, based on the total weight of the dehydration catalyst.

Alternative catalysts comprising: a) one or more anions selected fromthe group consisting of non-phosphorus-containing anions,heteropolyanions, and phosphate adducts, and b) one or more monovalentcations, wherein the catalyst is neutrally charged, can be utilized fordehydrating hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof to acrylic acid, acrylic acid derivatives, or mixturesthereof. Non limiting examples of non-phosphorus-containing anions arearsenates, condensed arsenates, nitrates, sulfates, condensed sulfates,borates, carbonates, chromates, condensed chromates, vanadates,niobates, tantalates, selenates, condensed silicates, condensedaluminates, germanates, condensed germanates, molybdates, condensedmolybdates, and other monomeric oxyanions or polyoxyanions that may beapparent to those having ordinary skill in the art. Non limitingexamples of heteropolyanions are heteropolyphosphates, such asarsenatophosphates, phosphoaluminates, phosphoborates, phosphochromates,phosphomolybdates, phosphosilicates, phosphosulfates, phosphotungstates,and others that may be apparent to those having ordinary skill in theart. Non limiting examples of phosphate adducts are adducts of phosphateanions with telluric acid, halides, borates, carbonates, nitrates,sulfates, chromates, silicates, oxalates, mixtures thereof, or othersthat may be apparent to those having ordinary skill in the art.

III. Catalyst Preparation Methods

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts; wherein said one or more precursor phosphatesalts consist essentially of: i) one or more cations, and ii) one ormore phosphate anions selected from the group represented by molecularformulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor;

wherein the water partial pressure in said gas mixture is equal to orgreater than the water partial pressure at the triple point of at leastone of said one or more precursor phosphate salts; wherein saidcontacting step between said dehydration catalyst precursor mixture andsaid gas mixture is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreprecursor phosphate salts; wherein one or more amorphous phosphate saltsare produced as a result of said one or more precursor phosphate saltsbeing contacted with said water vapor. In another embodiment of thepresent invention, said one or more cations are selected from the groupconsisting of monovalent cations, polyvalent cations, and mixturesthereof. In yet another embodiment of the present invention, said one ormore cations are selected from the group consisting of monovalentcations.

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts; wherein said one or more precursor phosphatesalts consist essentially of: i) one or more monovalent cations, and ii)one or more phosphate anions selected from the group represented bymolecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor;

wherein the water partial pressure in said gas mixture is equal to orgreater than the water partial pressure at the triple point of at leastone of said one or more precursor phosphate salts; wherein saidcontacting step between said dehydration catalyst precursor mixture andsaid gas mixture is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreprecursor phosphate salts; wherein one or more amorphous phosphate saltsare produced as a result of said one or more precursor phosphate saltsbeing contacted with said water vapor. In the context of the presentinvention, the anion represented by molecular formula (V) can refereither to the anion of cyclophosphate salts or to the anion oflong-chain linear polyphosphate salts as described in “Phosphoric Acidsand Phosphates, Kirk-Othmer Encyclopedia of Chemical Technology” byDavid R. Gard (published online: 15 Jul. 2005) and “Phosphorus:Chemistry, Biochemistrty and Technology” by D. E. C. Corbridge (2013).When the molecular formula (V) refers to the anion of long chainpolyphosphate salts, the molecular formula is not precise in that itdoes not include the minor perturbation of excess negative charge owingto the two end-group oxygens.

In the context of the present invention, the triple point is thetemperature and water partial pressure at which three phases:crystalline dihydrogen monophosphate or dihydrogen diphosphate salt,crystalline polyphosphate salt, and amorphous phosphate salt coexist inthermodynamic equilibrium. By way of example, and not limitation, thetriple point can be located by determining the interception of two (outof three) phase boundary curves in the water partial pressure versustemperature phase equilibrium diagram (see FIG. 2):

Curve A: phase boundary between i) crystalline dihydrogen monophosphateor crystalline dihydrogen diphosphate salt and ii) crystallinepolyphosphate salt, at low temperatures and water partial pressures(e.g. below about 248° C. and 0.85 bar for potassium salts, below about267° C. and 0.35 bar for cesium salts);

Curve B: phase boundary between i) crystalline polyphosphate salt andii) amorphous phosphate salt at high temperatures and medium waterpartial pressures (e.g. above about 248° C. and 0.85 bar for potassiumsalts, above about 267° C. and 0.35 bar for cesium salts); and

Curve C: phase boundary between i) crystalline dihydrogen monophosphateor crystalline dihydrogen diphosphate salt and ii) amorphous phosphatesalt at high temperatures and high water partial pressures.

The phase boundary curves can be determined by any method known to thoseskilled in the art, such as, by way of example and not limitation,in-situ x-ray diffraction (XRD), thermal analysis (e.g.thermogravimetric analysis, differential thermal analysis, anddifferential scanning calorimetry), Raman spectroscopy, infraredspectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, or themethods described in Taninouchi, Y.-k., et al., J. Electrochem. Soc.156:B572-B579 (2009); or Ikeda, A. and Haile, S. M., Solid State Ionics2012, 213:63-71 (2012) (all incorporated herein by reference). As anillustration, in a method based on the in-situ XRD technique, aprecursor phosphate salt is contacted at high temperature (e.g. 450° C.)with a gas stream consisting of an inert gas (e.g. nitrogen, helium, orair) and water vapor at a specific water partial pressure untilequilibrium is achieved. Then, the temperature is gradually decreasedwhile monitoring changes on x-ray diffraction patterns, until a phasetransition is observed. The same procedure is repeated at differentwater partial pressures and the transition temperatures are recorded.The water partial pressures (in logarithmic scale) are plotted againstthe transition temperatures (in linear scale) and fitted to theArrhenius equation (log₁₀(P_(H) ₂ _(O))=A+B/T). Finally, the triplepoint is calculated by determining the interception point between thetwo phase boundary curves (i.e. curve A and curve B in FIG. 2).

In one embodiment of the present invention, the temperature during saidcontacting step between said dehydration catalyst precursor mixture andsaid gas mixture is equal to or greater than the temperature at thetriple point of at least one of said one or more precursor phosphatesalts. In another embodiment of the present invention, the temperatureduring said contacting step between said dehydration catalyst precursormixture and said gas mixture is equal to or greater than the lowesttriple point temperature of said one or more precursor phosphate salts.In another embodiment of the present invention, the temperature duringsaid contacting step between said dehydration catalyst precursor mixtureand said gas mixture is equal to or greater than the highest triplepoint temperature of said one or more precursor phosphate salts. Inanother embodiment of the present invention, the temperature during saidcontacting step between said dehydration catalyst precursor mixture andsaid gas mixture is equal to or greater than the average temperaturebetween the lowest triple point temperature and the highest triple pointtemperature of said one or more precursor phosphate salts. In anotherembodiment of the present invention, the temperature during saidcontacting step between said dehydration catalyst precursor mixture andsaid gas mixture is at least 10° C. greater than the temperature at thetriple point of at least one of said one or more precursor phosphatesalts. In another embodiment of the present invention, the temperatureduring said contacting step between said dehydration catalyst precursormixture and said gas mixture is at least 50° C. greater than thetemperature at the triple point of at least one of said one or moreprecursor phosphate salts. In another embodiment of the presentinvention, the temperature during said contacting step between saiddehydration catalyst precursor mixture and said gas mixture is at least100° C. greater than the temperature at the triple point of at least oneof said one or more precursor phosphate salts.

In one embodiment of the present invention, the water partial pressurein said gas mixture is equal to or greater than the water partialpressure at the triple point of at least one of said one or moreprecursor phosphate salts. In another embodiment of the presentinvention, the water partial pressure in said gas mixture is equal to orgreater than the lowest triple point water partial pressure of said oneor more precursor phosphate salts. In another embodiment of the presentinvention, the water partial pressure in said gas mixture is equal to orgreater than the highest triple point water partial pressure of said oneor more precursor phosphate salts. In another embodiment of the presentinvention, the water partial pressure in said gas mixture is equal to orgreater than the average water partial pressure between the lowesttriple point water partial pressure and the highest triple point waterpartial pressure of said one or more precursor phosphate salts. In oneembodiment of the present invention, the water partial pressure in saidgas mixture is at least 1 bar greater than the water partial pressure atthe triple point of at least one of said one or more precursor phosphatesalts. In one embodiment of the present invention, the water partialpressure in said gas mixture is at least 2 bar greater than the waterpartial pressure at the triple point of at least one of said one or moreprecursor phosphate salts. In one embodiment of the present invention,the water partial pressure in said gas mixture is at least 5 bar greaterthan the water partial pressure at the triple point of at least one ofsaid one or more precursor phosphate salts.

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts; wherein said one or more precursor phosphatesalts consist essentially of: i) one or more monovalent cations, and ii)one or more phosphate anions selected from the group represented bymolecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor at a partial pressure equal toor greater than about 4 bar;

wherein said contacting step between said dehydration catalyst precursormixture and said gas mixture is performed at a temperature equal to orgreater than about 250° C.; wherein one or more amorphous phosphatesalts are produced as a result of said one or more precursor phosphatesalts being contacted with said water vapor.

In another embodiment of the present invention, the method of preparingthe dehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts; wherein said one or more precursor phosphatesalts consist essentially of: i) one or more monovalent cations selectedfrom the group consisting of Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof;and ii) one or more phosphate anions selected from the group representedby molecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor at a partial pressure equal toor greater than about 0.8 bar;

wherein said contacting step between said dehydration catalyst precursormixture and said gas mixture is performed at a temperature equal to orgreater than about 250° C.; wherein one or more amorphous phosphatesalts are produced as a result of said one or more precursor phosphatesalts being contacted with said water vapor.

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts and one or more non-phosphate compounds;wherein said one or more non-phosphate compounds are substantiallychemically inert to said one or more precursor phosphate salts; whereinsaid one or more precursor phosphate salts consist essentially of: i)one or more cations, and ii) one or more phosphate anions selected fromthe group represented by molecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor;

wherein the water partial pressure in said gas mixture is equal to orgreater than the water partial pressure at the triple point of at leastone of said one or more precursor phosphate salts; wherein saidcontacting step between said dehydration catalyst precursor mixture andsaid gas mixture is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreprecursor phosphate salts; wherein one or more amorphous phosphate saltsare produced as a result of said one or more precursor phosphate saltsbeing contacted with said water vapor. In another embodiment of thepresent invention, said one or more cations are selected from the groupconsisting of monovalent cations, polyvalent cations, and mixturesthereof. In yet another embodiment of the present invention, said one ormore cations are selected from the group consisting of monovalentcations.

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts and one or more non-phosphate compounds;wherein said one or more non-phosphate compounds are substantiallychemically inert to said one or more precursor phosphate salts; whereinsaid one or more precursor phosphate salts consist essentially of: i)one or more monovalent cations, and ii) one or more phosphate anionsselected from the group represented by molecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor;

wherein the water partial pressure in said gas mixture is equal to orgreater than the water partial pressure at the triple point of at leastone of said one or more precursor phosphate salts; wherein saidcontacting step between said dehydration catalyst precursor mixture andsaid gas mixture is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreprecursor phosphate salts; wherein one or more amorphous phosphate saltsare produced as a result of said one or more precursor phosphate saltsbeing contacted with said water vapor. In another embodiment of thepresent invention, said one or more non-phosphate compounds areessentially chemically inert to said one or more precursor phosphatesalts. In yet another embodiment of the present invention, said one ormore non-phosphate compounds are chemically inert to said one or moreprecursor phosphate salts.

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts and one or more non-phosphate compounds;wherein said one or more non-phosphate compounds are substantiallychemically inert to said one or more precursor phosphate salts; whereinsaid one or more precursor phosphate salts consist essentially of: i)one or more monovalent cations, and ii) one or more phosphate anionsselected from the group represented by molecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor;

wherein the water partial pressure in said gas mixture is equal to orgreater than about 4 bar; wherein said contacting step between saiddehydration catalyst precursor mixture and said gas mixture is performedat a temperature equal to or greater than about 250° C.; wherein one ormore amorphous phosphate salts are produced as a result of said one ormore precursor phosphate salts being contacted with said water vapor. Inanother embodiment of the present invention, said one or morenon-phosphate compounds are essentially chemically inert to said one ormore precursor phosphate salts. In yet another embodiment of the presentinvention, said one or more non-phosphate compounds are chemically inertto said one or more precursor phosphate salts.

In another embodiment of the present invention, the method of preparingthe dehydration catalyst comprises contacting:

(a) a dehydration catalyst precursor mixture comprising one or moreprecursor phosphate salts and one or more non-phosphate compounds;wherein said one or more non-phosphate compounds are substantiallychemically inert to said one or more precursor phosphate salts; whereinsaid one or more precursor phosphate salts consist essentially of: i)one or more monovalent cations selected from the group consisting ofNa⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof, and ii) one or more phosphateanions selected from the group represented by molecular formulae (IV)and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V);

wherein y is any integer equal to or greater than 1 and z is any integerequal to or greater than 3; wherein said one or more precursor phosphatesalts are neutrally charged; with

(b) a gas mixture comprising water vapor;

wherein the water partial pressure in said gas mixture is equal to orgreater than about 0.8 bar; wherein said contacting step between saiddehydration catalyst precursor mixture and said gas mixture is performedat a temperature equal to or greater than about 250° C.; wherein one ormore amorphous phosphate salts are produced as a result of said one ormore precursor phosphate salts being contacted with said water vapor. Inanother embodiment of the present invention, said one or morenon-phosphate compounds are essentially chemically inert to said one ormore precursor phosphate salts. In yet another embodiment of the presentinvention, said one or more non-phosphate compounds are chemically inertto said one or more precursor phosphate salts.

In one embodiment of the present invention, the weight ratio between thetotal amount of said one or more precursor phosphate salts and the totalamount of said one or more non-phosphate compounds in said dehydrationcatalyst precursor mixture is between about 1:10 and about 4:1.

In the context of the present invention, “one or more cations” refers todifferent types of cations and “one or more anions” refers to differenttypes of anions. Non limiting examples of cations are metallic cations,organo-metallic cations, ammonium, substituted ammonium, oxycations, andother cations known by those skilled in the art. Non limiting examplesof substituted ammonium and other cations are isopropylammonium,ethylenediammonium, sarcosinium, L-histidinium, glycinium, and4-aminopyridinium. Non limiting examples of oxycations are pervanadyland vanadyl ions.

Non limiting examples of monovalent cations of said one or moreprecursor phosphate salts are cations of alkali metals, organo-metalliccations, ammonium, substituted ammonium, oxycations (e.g. pervanadyl),and other cations known by those skilled in the art. In one embodimentof the present invention, said one or more monovalent cations of saidone or more precursor phosphate salts are selected from the groupconsisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, and mixtures thereof. Inanother embodiment of the present invention, said one or more monovalentcations of said one or more precursor phosphate salts are selected fromthe group consisting of Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof. In yetanother embodiment of the present invention, said one or more monovalentcations is K⁺.

In another embodiment of the present invention, at least one of said oneor more precursor phosphate salts consists of two or more differentmonovalent cations selected from the group consisting of Li⁺, Na⁺, K⁺,Rb⁺, Cs⁺, Ag⁺, and Tl⁺. In another embodiment of the present invention,at least one of said one or more precursor phosphate salts consists oftwo or more different monovalent cations selected from the groupconsisting of Na⁺, K⁺, Rb⁺, and Cs⁺.

In one embodiment of the present invention, said one or more phosphateanions of said one or more precursor phosphate salts are selected fromthe group represented by molecular formulae (IVa), (IVb), (IVc), (IVd),(Va), (Vb), (Vc) and mixtures thereof:[H₂PO₄]⁻  (IVa)[H₂P₂O₇]²⁻  (IVb)[H₂P₃O₁₀]³⁻  (IVc)[H₂P₄O₁₃]⁴⁻  (IVd)[P₃O₉]³⁻  (Va)[P₆O₁₈]⁶⁻  (Vb)[PO₃]_(n) ^(n−)  (Vc);

wherein n is any integer equal to or greater than 3. In the context ofthe present invention, the anion represented by molecular formula (Vc)can refer either to the anion of cyclophosphate salts or to the anion oflong-chain linear polyphosphate salts as described in “Phosphoric Acidsand Phosphates, Kirk-Othmer Encyclopedia of Chemical Technology” byDavid R. Gard (published online: 15 Jul. 2005) and “Phosphorus:Chemistry, Biochemistrty and Technology” by D. E. C. Corbridge (2013).When the molecular formula (Vc) refers to the anion of long chainpolyphosphate salts, the molecular formula is not precise in that itdoes not include the minor perturbation of excess negative charge owingto the two end-group oxygens.

Non limiting examples of precursor phosphate salts are dihydrogenmonophosphates, dihydrogen diphosphates, dihydrogen triphosphates,dihydrogen tetraphosphates, tricyclophosphates, tetracyclophosphates,pentacyclophosphates, hexacyclophosphates, octacyclophosphates,decacyclophosphates, and linear polyphosphates of alkali metals or mixedalkali metals. In one embodiment of the present invention, said one ormore precursor phosphate salts are selected from the group consisting ofLiH₂PO₄, Li₂H₂P₂O₇, Li₃P₃O₉, Li₄P₄O₁₂, Li₆P₆O₁₈, Li₈P₈O₂₄, (LiPO₃)_(n),NaH₂PO₄, Na₂H₂P₂O₇, Na₃H₂P₃O₁₀, Na₃P₃O₉, Na₅P₅O₁₅, Na₄P₄O₁₂, Na₆P₆O₁₈,Na₈P₈O₂₄, Na₁₂P₁₂O₃₆, (NaPO₃)_(n), KH₂PO₄, K₂H₂P₂O₇, K₃H₂P₃O₁₀,K₄H₂P₄O₁₃, K₃P₃O₉, K₄P₄O₁₂, K₆P₆O₁₈, K₈P₈O₂₄, K₁₀P₁₀O₃₀, (KPO₃)_(n),RbH₂PO₄, Rb₂H₂P₂O₇, Rb₃H₂P₃O₁₀, Rb₄H₂P₄O₁₃, Rb₃P₃O₉, Rb₄P₄O₁₂, Rb₆P₆O₁₈,Rb₈P₈O₂₄, (RbPO₃)_(n), CsH₂PO₄, Cs₂H₂P₂O₇, Cs₃H₂P₃O₁₀, Cs₄H₂P₄O₁₃,Cs₃P₃O₉, Cs₄P₄O₁₂, Cs₆P₆O₁₈, Cs₈P₈O₂₄, (CsPO₃)_(n), NaK₃(H₂P₂O₇)₂,LiK₂P₃O₉, LiNa₂P₃O₉, Na₂KP₃O₉, Na₂RbP₃O₉, Na₂CsP₃O₉, Na₃KP₄O₁₂,Na₂K₂P₄O₁₂, Na₂Rb₂P₄O₁₂, Na₃CsP₄O₁₂, Li₃Na₃P₆O₁₈, Li₃K₃P₆O₁₈,Li₂K₄P₆O₁₈, Li₃Na₃P₆O₁₈, Li₃K₃P₆O₁₈, Li₃Rb₃P₆O₁₈, Li₃Cs₃P₆O₁₈,Na₄Rb₂P₆O₁₈, Na₄Cs₂P₆O₁₈, LiNa₇P₈O₂₄, Na₆K₄P₁₀O₃₀, (LiK(PO₃)₂)_(n),(LiRb(PO₃)₂)_(n), (Li₂Rb(PO₃)₃)_(n), (LiCs(PO₃)₂)_(n),(Li₂Cs(PO₃)₃)_(n), any of their hydrated forms, and mixtures thereof. Inanother embodiment of the present invention, said one or more precursorphosphate salts are selected from the group consisting of LiH₂PO₄,(LiPO₃)_(n), NaH₂PO₄, (NaPO₃)_(n), KH₂PO₄, (KPO₃)_(n), RbH₂PO₄,(RbPO₃)_(n), CsH₂PO₄, (CsPO₃)_(n), any of their hydrated forms, andmixtures thereof. In yet another embodiment of the present invention,said one or more precursor phosphate salts are selected from the groupconsisting of KH₂PO₄, (KPO₃)_(n), any of their hydrated forms, andmixtures thereof. In the context of the present invention, the precursorphosphate salts represented by the formulae (M^(I)PO₃)_(n),(M^(I)N^(I)(PO₃)₂)_(n), or (M^(I) ₂N^(I)(PO₃)₃)_(n), wherein M^(I) andN^(I) are two different monovalent cations, can be eithercyclophosphates or long-chain linear polyphosphates.

In one embodiment of the present invention, said one or morenon-phosphate compounds comprise silicon oxide (SiO₂). In one embodimentof the present invention, said one or more non-phosphate compoundsconsists essentially of silicon oxide (SiO₂). In another embodiment ofthe present invention, said silicon oxide is selected from the groupconsisting of amorphous silica, quartz, tridymite, cristobalite,moganite, coesite, and mixtures thereof. In another embodiment of thepresent invention, said silicon oxide is amorphous silica. In yetanother embodiment of the present invention, said silicon oxide has aspecific surface area of less than about 10 m²/g.

In another embodiment of the present invention, said one or moreprecursor phosphate salts are selected from the group consisting ofLiH₂PO₄, (LiPO₃)_(n), NaH₂PO₄, (NaPO₃)_(n), KH₂PO₄, (KPO₃)_(n), RbH₂PO₄,(RbPO₃)_(n), CsH₂PO₄, (CsPO₃)_(n), any of their hydrated forms, andmixtures thereof; and said one or more non-phosphate compounds areselected from the group consisting of amorphous silica, quartz, andmixtures thereof. In another embodiment of the present invention, saidone or more precursor phosphate salts is KH₂PO₄ or (KPO₃)_(n), and saidone or more non-phosphate compounds is amorphous silica.

In one embodiment of the present invention, said one or morenon-phosphate compounds comprise one or more oxysalts comprising: (a)one or more polyvalent cations, and (b) one or more oxyanions selectedfrom the group represented by molecular formulae (II) and (III):[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−)  (II)[Ta_(2d)O_((5d+e))]^(2e−)  (III);wherein a and b are positive integers or zero; wherein c, d, and e arepositive integers; wherein (a−2b) is equal to or greater than zero;wherein (2c−a) is greater than zero; wherein said one or more oxysaltsare neutrally charged. In another embodiment of the present invention,said one or more non-phosphate compounds further comprise silicon oxide(SiO₂).

In another embodiment of the present invention, said one or morenon-phosphate compounds comprise one or more oxysalts comprising: (a)one or more polyvalent cations, (b) one or more monovalent cations, and(c) one or more oxyanions selected from the group represented bymolecular formulae (II) and (III):[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−)  (II)[Ta_(2d)O_((5d+e))]^(2e−)  (III);wherein a and b are positive integers or zero; wherein c, d, and e arepositive integers; wherein (a−2b) is equal to or greater than zero;wherein (2c−a) is greater than zero; wherein said one or more oxysaltsare neutrally charged. In another embodiment of the present invention,said one or more non-phosphate compounds further comprise silicon oxide(SiO₂).

Non limiting examples of said one or more polyvalent cations of said oneor more oxysalts are cations of alkaline earth metals, transitionmetals, post-transition or poor metals, and metalloids; organo-metalliccations, substituted ammonium cations, oxycations (e.g. vanadyl), andother cations known by those skilled in the art. In one embodiment ofthe present invention, said one or more polyvalent cations of said oneor more oxysalts are selected from the group consisting of the cationsof the metals Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W, Mn, Re, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, Bi, La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof. In anotherembodiment of the present invention, said one or more polyvalent cationsof said one or more oxysalts are selected from the group consisting ofthe cations of the metals Mg, Ca, Sr, Ba, Y, Mn, Al, Er, and mixturesthereof. In another embodiment of the present invention, said one ormore polyvalent cations of said one or more oxysalts are selected fromthe group consisting of divalent cations, trivalent cations, tetravalentcations, pentavalent cations, and mixtures thereof. In anotherembodiment of the present invention, said one or more polyvalent cationsof said one or more oxysalts are selected from the group consisting ofBe²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Sc³⁺, Y³⁺, Ti³⁺, Ti⁴⁺, Zr²⁺, Zr⁴⁺, Hf⁴⁺,V³⁺, V⁴⁺, Nb³⁺, Cr²⁺, Cr³⁺, Mo³⁺, Mo⁴⁺, Mn²⁺, Mn³⁺, Re⁴⁺, Al³⁺, Ga³⁺,In³⁺, Si⁴⁺, Ge⁴⁺, Sn⁴⁺, Pb⁴⁺, Sb³⁺, Sb⁵⁺, Bi³⁺, La³⁺, Ce³⁺, Ce⁴⁺, Pr³⁺,Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺, andmixtures thereof. In another embodiment of the present invention, saidone or more polyvalent cations of said one or more oxysalts are selectedfrom the group consisting of Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Y³⁺, Mn²⁺, Mn³⁺,Al³⁺, Er³⁺, and mixtures thereof. In yet another embodiment of thepresent invention, said one or more polyvalent of said one or moreoxysalts cations is Ba²⁺.

Non limiting examples of said one or more monovalent cations of said oneor more oxysalts are cations of alkali metals. In one embodiment of thepresent invention, said one or more monovalent cations of said one ormore oxysalts are selected from the group consisting of the cations ofthe metals Li, Na, K, Rb, Cs, Ag, Tl, and mixtures thereof; and said oneor more polyvalent cations of said one or more oxysalts are selectedfrom the group consisting of the cations of the metals Be, Mg, Ca, Sr,Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Al, Ga, In, Tl, Si,Ge, Sn, Pb, Sb, Bi, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,Lu, and mixtures thereof. In another embodiment of the presentinvention, said one or more monovalent cations of said one or moreoxysalts are selected from the group consisting of the cations of themetals K, Rb, Cs, and mixtures thereof; and said one or more polyvalentcations of said one or more oxysalts are selected from the groupconsisting of the cations of the metals Mg, Ca, Sr, Ba, Y, Mn, Al, Er,and mixtures thereof.

In another embodiment of the present invention, said one or moreoxyanions of said one or more oxysalts are selected from the grouprepresented by molecular formulae (IIa) to (IId), (IIIa) to (IIIg), andmixtures thereof:[SO₄]²⁻  (IIa)[S₂O₇]²⁻  (IIb)[HSO₄]¹⁻  (IIc)[SO₄]²⁻.[HSO₄]⁻  (IId)[Ta₂O₆]²⁻  (IIIa)[Ta₂O₇]⁴⁻  (IIIb)[Ta₂O₉]⁸⁻  (IIIc)[Ta₂O₁₀]¹⁰⁻  (IIId)[Ta₂O₁₁]¹²⁻  (IIIe)[Ta₄O₁₁]²⁻  (IIIf)[Ta₄O₁₅]¹⁰⁻  (IIIg).

In another embodiment of the present invention, said one or moreoxyanions of said one or more oxysalts are selected from the grouprepresented by molecular formulae (IIa), (IIIa), and mixtures thereof:[SO₄]²⁻  (IIa)[Ta₂O₆]²⁻  (IIIa).

Non limiting examples of said one or more oxysalts are sulfates ofalkaline-earth metals, tantalates of alkaline-earth metals, sulfates ofmixed alkali and alkaline earth metals, and tantalates of mixed alkaliand alkaline earth metals. In one embodiment of the present invention,said one or more oxysalts are selected from the group consisting ofCaSO₄, SrSO₄, BaSO₄, SrK₂(SO₄)₂, SrRb₂(SO₄)₂, Ca₂K₂(SO₄)₃, Ca₂Rb₂(SO₄)₃,Ca₂Cs₂(SO₄)₃, CaTa₄O₁₁, SrTa₄O₁₁, BaTa₄O₁₁, MgTa₂O₆, CaTa₂O₆, SrTa₂O₆,BaTa₂O₆, Mg₂Ta₂O₇, Ca₂Ta₂O₇, Sr₂Ta₂O₇, SrK₂Ta₂O₇, Ba₂Ta₂O₇, Ba₃Ta₂O₈,Mg₄Ta₂O₉, Ca₄Ta₂O₉, Sr₄Ta₂O₉, Ba₄Ta₂O₉, Ca₅Ta₂O₁₀, Ca₂KTa₃O₁₀,Ca₂RbTa₃O₁₀, Ca₂CsTa₃O₁₀, Sr₂KTa₃O₁₀, Sr₂RbTa₃O₁₀, Sr₂CsTa₃O₁₀,Mg₅Ta₄O₁₅, Sr₅Ta₄O₁₅, Ba₅Ta₄O₁₅, Sr₂KTa₅O₁₅, Ba₂KTa₅O₁₅, Sr₆Ta₂O₁₁,Ba₆Ta₂O₁₁, any of their hydrated forms, and mixtures thereof. In anotherembodiment of the present invention, said one or more oxysalts areselected from the group consisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆,BaSO₄, BaTa₂O₆, any of their hydrated forms, and mixtures thereof. Inyet another embodiment of the present invention, said one or moreoxysalts are selected from the group consisting of BaSO₄, BaTa₂O₆, anyof their hydrated forms, and mixtures thereof.

In one embodiment of the present invention, said one or more precursorphosphate salts are selected from the group consisting of LiH₂PO₄,(LiPO₃)_(n), NaH₂PO₄, (NaPO₃)_(n), KH₂PO₄, (KPO₃)_(n), RbH₂PO₄,(RbPO₃)_(n), CsH₂PO₄, (CsPO₃)_(n), any of their hydrated forms, andmixtures thereof; and said one or more non-phosphate compounds areselected from the group consisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆,BaSO₄, BaTa₂O₆, any of their hydrated forms, and mixtures thereof. Inanother example of the present invention, said one or more precursorphosphate salts is KH₂PO₄ or (KPO₃)_(n) and said one or morenon-phosphate compounds is BaSO₄.

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises:

(a) mixing two or more different phosphate precursor compounds selectedfrom the group comprising:M_(j) ^(I)(H_((2+i−j))P_(i)O_((3i+1)))  (VIa)(NH₄)_(l)(H_((2+k−l))P_(k)O_((3k+1)))  (VIb)M_(p) ^(I)(H_((m−p))(PO₃)_(m))  (VIc)(NH₄)_(r)(H_((q−r))(PO₃)_(q))  (VId)M_(u) ^(I)(H_((t−u))P_((2s+t))O_((5s+3t)))  (VIe)(NH₄)_(α)(H_((w−α))P_((2v+w))O_((5v+3w)))  (VIf)M₂ ^(I)O  (VIg)M^(I)OH  (VIh)M^(I)NO₃  (VIi)M^(I) ₂CO₃  (VIj)(H(CH₂)_(β)COO)M^(I)  (VIk);

to produce a dehydration catalyst precursor mixture; wherein M^(I) is amonovalent cation; wherein said monovalent cation is selected from thegroup consisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, and mixturesthereof; wherein i, k, m, q, s, and v are integers greater than zero;wherein j, l, p, r, u, and α are real numbers equal to or greater thanzero; wherein t, w, and β are integers equal to or greater than zero;wherein (2+i−j), (2+k−l), (m−p), (q−r), (t−u), and (w−α) are equal to orgreater than zero; wherein the molar ratio between the total amount ofphosphorus (P) and the total amount of said one or more monovalentcations (M^(I)) in said dehydration catalyst precursor mixture is about1; and

(b) contacting said dehydration catalyst precursor mixture with a gasmixture comprising water vapor to produce one or more amorphousphosphate salts; wherein the water partial pressure in said gas mixtureis equal to or greater than the water partial pressure at the triplepoint of at least one of said one or more amorphous phosphate salts; andwherein said contacting step between said dehydration catalyst precursormixture and said gas mixture is performed at a temperature equal to orgreater than the temperature at the triple point of at least one of saidone or more amorphous phosphate salts.

In one embodiment of the present invention, the method of preparing thedehydration catalyst comprises:

(a) mixing two or more different phosphate precursor compounds selectedfrom the group comprising:M_(j) ^(I)(H_((2+i−j))P_(i)O_((3i+1)))  (VIa)(NH₄)_(l)(H_((2+k−l))P_(k)O_((3k+1)))  (VIb)M_(p) ^(I)(H_((m−p))(PO₃)_(m))  (VIc)(NH₄)_(r)(H_((q−r))(PO₃)_(q))  (VId)M_(u) ^(I)(H_((t−u))P_((2s+t))O_((5s+3t)))  (VIe)(NH₄)_(α)(H_((w−α))P_((2v+w))O_((5v+3w)))  (VIf)M₂ ^(I)O  (VIg)M^(I)OH  (VIh)M^(I)NO₃  (VIi)M^(I) ₂CO₃  (VIj)(H(CH₂)_(β)COO)M^(I)  (VIk);

to produce a dehydration catalyst precursor mixture; wherein M^(I) is amonovalent cation; wherein said monovalent cation is selected from thegroup consisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, and mixturesthereof; wherein i, k, m, q, s, and v are integers greater than zero;wherein j, l, p, r, u, and α are real numbers equal to or greater thanzero; wherein t, w, and β are integers equal to or greater than zero;wherein (2+i−j), (2+k−l), (m−p), (q−r), (t−u), and (w−α) are equal to orgreater than zero; wherein the ratio between the total molar amount ofphosphorus (P) and the total molar amount of said one or more monovalentcations (M^(I)) in said dehydration catalyst precursor mixture is about1; and

(b) contacting said dehydration catalyst precursor mixture with a gasmixture comprising water vapor at a partial pressure equal to or greaterthan about 4 bar; wherein said contacting step between said dehydrationcatalyst precursor mixture and said gas mixture is performed at atemperature equal to or greater than about 250° C.; wherein one or moreamorphous phosphate salts are produced as a result of said dehydrationcatalyst precursor mixture being contacted with said water vapor.

In another embodiment of the present invention, the method of preparingthe dehydration catalyst comprises:

(a) mixing two or more different phosphate precursor compounds selectedfrom the group comprising:M_(j) ^(I)(H_((2+i−j))P_(i)O_((3i+1)))  (VIa)(NH₄)_(l)(H_((2+k−l))P_(k)O_((3k+1)))  (VIb)M_(p) ^(I)(H_((m−p))(PO₃)_(m))  (VIc)(NH₄)_(r)(H_((q−r))(PO₃)_(q))  (VId)M_(u) ^(I)(H_((t−u))P_((2s+t))O_((5s+3t)))  (VIe)(NH₄)_(α)(H_((w−α))P_((2v+w))O_((5v+3w)))  (VIf)M₂ ^(I)O  (VIg)M^(I)OH  (VIh)M^(I)NO₃  (VIi)M^(I) ₂CO₃  (VIj)(H(CH₂)_(β)COO)M^(I)  (VIk);

to produce a dehydration catalyst precursor mixture; wherein M^(I) is amonovalent cation; wherein said monovalent cation is selected from thegroup consisting of Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof; wherein i,k, m, q, s, and v are integers greater than zero; wherein j, l, p, r, u,and α are real numbers equal to or greater than zero; wherein t, w, andβ are integers equal to or greater than zero; wherein (2+i−j), (2+k−l),(m−p), (q−r), (t−u), and (w−α) are equal to or greater than zero;wherein the ratio between the total molar amount of phosphorus (P) andthe total molar amount of said one or more monovalent cations (M^(I)) insaid dehydration catalyst precursor mixture is about 1; and

(b) contacting said dehydration catalyst precursor mixture with a gasmixture comprising water vapor at a partial pressure equal to or greaterthan about 0.8 bar; wherein said contacting step between saiddehydration catalyst precursor mixture and said gas mixture is performedat a temperature equal to or greater than about 250° C.; wherein one ormore amorphous phosphate salts are produced as a result of saiddehydration catalyst precursor mixture being contacted with said watervapor.

In another embodiment of the present invention, said two or moredifferent phosphate precursor compounds are selected form the groupconsisting of H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄, P₂O₅, Li₂HPO₄,Li₃PO₄, Li₄P₂O₇, Li₂O, LiOH, LiNO₃, Li₂CO₃, (CH₃COO)Li, HCOOLi, Na₂HPO₄,Na₃PO₄, Na₄P₂O₇, Na₂O, NaOH, NaNO₃, Na₂CO₃, (CH₃COO)Na, HCOONa, K₂HPO₄,K₃PO₄, K₄P₂O₇, K₂O, KOH, KNO₃, K₂CO₃, (CH₃COO)K, HCOOK, Rb₂HPO₄, Rb₃PO₄,Rb₄P₂O₇, Rb₂O, RbOH, RbNO₃, Rb₂CO₃, (CH₃COO)Rb, HCOORb, Cs₂HPO₄, Cs₃PO₄,Cs₄P₂O₇, Cs₂O, CsOH, CsNO₃, Cs₂CO₃, (CH₃COO)Cs, HCOOCs, any of theirhydrated forms, and mixtures thereof.

In another embodiment of the present invention, the method of preparingthe dehydration catalyst further comprises mixing one or morenon-phosphate compounds with said two or more different phosphateprecursor compounds before said contacting step; wherein said one ormore non-phosphate compounds are substantially chemically inert to saidtwo or more different phosphate precursor compounds. In anotherembodiment of the present invention, said one or more non-phosphatecompounds are essentially chemically inert to said two or more differentphosphate precursor compounds. In another embodiment of the presentinvention, said one or more non-phosphate compounds are chemically inertto said two or more different phosphate precursor compounds. In anotherembodiment of the present invention, said one or more non-phosphatecompounds comprise silicon oxide (SiO₂). In another embodiment of thepresent invention, said one or more non-phosphate compounds consistsessentially of silicon oxide (SiO₂). In another embodiment of thepresent invention, said silicon oxide is selected from the groupconsisting of amorphous silica, quartz, tridymite, cristobalite,moganite, coesite, and mixtures thereof. In another embodiment of thepresent invention, said one or more non-phosphate compounds comprise oneor more oxysalts comprising: (a) one or more polyvalent cations, and (b)one or more oxyanions selected from the group represented by molecularformulae (II) and (III):[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−)  (II)[Ta_(2d)O_((5d+e))]^(2e−)  (III);wherein a and b are positive integers or zero; wherein c, d, and e arepositive integers; wherein (a−2b) is equal to or greater than zero;wherein (2c−a) is greater than zero; wherein said one or more oxysaltsare neutrally charged.

In another embodiment of the present invention, said two or moredifferent phosphate precursor compounds are selected form the groupconsisting of H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄, P₂O₅, Li₂HPO₄,Li₃PO₄, Li₄P₂O₇, Li₂O, LiOH, LiNO₃, Li₂CO₃, (CH₃COO)Li, HCOOLi, Na₂HPO₄,Na₃PO₄, Na₄P₂O₇, Na₂O, NaOH, NaNO₃, Na₂CO₃, (CH₃COO)Na, HCOONa, K₂HPO₄,K₃PO₄, K₄P₂O₇, K₂O, KOH, KNO₃, K₂CO₃, (CH₃COO)K, HCOOK, Rb₂HPO₄, Rb₃PO₄,Rb₄P₂O₇, Rb₂O, RbOH, RbNO₃, Rb₂CO₃, (CH₃COO)Rb, HCOORb, Cs₂HPO₄, Cs₃PO₄,Cs₄P₂O₇, Cs₂O, CsOH, CsNO₃, Cs₂CO₃, (CH₃COO)Cs, HCOOCs, any of theirhydrated forms, and mixtures thereof; and said one or more non-phosphatecompounds are selected from the group consisting of amorphous silica,quartz, and mixtures thereof.

In another embodiment of the present invention, said two or moredifferent phosphate precursor compounds are selected form the groupconsisting of H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄, P₂O₅, Li₂HPO₄,Li₃PO₄, Li₄P₂O₇, Li₂O, LiOH, LiNO₃, Li₂CO₃, (CH₃COO)Li, HCOOLi, Na₂HPO₄,Na₃PO₄, Na₄P₂O₇, Na₂O, NaOH, NaNO₃, Na₂CO₃, (CH₃COO)Na, HCOONa, K₂HPO₄,K₃PO₄, K₄P₂O₇, K₂O, KOH, KNO₃, K₂CO₃, (CH₃COO)K, HCOOK, Rb₂HPO₄, Rb₃PO₄,Rb₄P₂O₇, Rb₂O, RbOH, RbNO₃, Rb₂CO₃, (CH₃COO)Rb, HCOORb, Cs₂HPO₄, Cs₃PO₄,Cs₄P₂O₇, Cs₂O, CsOH, CsNO₃, Cs₂CO₃, (CH₃COO)Cs, HCOOCs, any of theirhydrated forms, and mixtures thereof; and said one or more non-phosphatecompounds are selected from the group consisting of CaSO₄, CaTa₂O₆,SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any of their hydrated forms, andmixtures thereof.

In one embodiment of the present invention, at least one of said one ormore precursor phosphate salts of said dehydration catalyst precursormixture is a hydrated salt. In another embodiment of the presentinvention, at least one of said one or more non-phosphate compounds ofsaid dehydration catalyst precursor mixture is a hydrated compound. Inanother embodiment of the present invention, at least one of said one ormore oxysalts of said dehydration catalyst precursor mixture is ahydrated salt. In another embodiment of the present invention, at leastone of said two or more different phosphate precursor compounds of saiddehydration catalyst precursor mixture is a hydrated compound. Ahydrated salt or compound contains a specific number of water moleculesper formula unit of the salt or compound. Non limiting examples ofhydrated salts or compounds are hemihydrated, monohydrated,sesquihydrated, dehydrated, trihydrated, tetrahydrated, pentahydrated,hexahydrated, heptahydrated, octahydrated, nonahydrated, nonahydrated,and decahydrated salts or compounds.

In one embodiment of the present invention, the method of preparing thedehydration catalyst further comprises mixing one or more inert supportswith said one or more precursor phosphate salts, said two or moredifferent phosphate precursor compounds, or said dehydration catalystprecursor mixture before said contacting step with said gas mixture. Inanother embodiment of the present invention, said one or morenon-phosphate compounds in said method of preparing the dehydrationcatalyst consist essentially of one or more inert supports. Non limitingexamples of inert supports are silica or silicates, alumina oraluminates, aluminosilicates, titania or titanates, zirconia orzirconates, carbons (such as activated carbon, diamond, graphite, orfullerenes), phosphates, sulfates, tantalates, ceria, other metaloxides, and mixtures thereof. In the context of the reactions expresslydescribed herein, in one embodiment of the present invention, said oneor more inert supports comprise silicon oxide (SiO₂). In anotherembodiment of the present invention, said one or more inert supportsconsists essentially of silicon oxide (SiO₂). In another embodiment ofthe present invention, said silicon oxide is selected from the groupconsisting of amorphous silica, quartz, tridymite, cristobalite,moganite, coesite, and mixtures thereof. In another embodiment of thepresent invention, said silicon oxide is amorphous silica. In anotherembodiment of the present invention, said silicon oxide has a specificsurface area of less than about 10 m²/g.

The method of preparing the dehydration catalyst comprises contactingsaid dehydration catalyst precursor mixture with a gas mixturecomprising water vapor. In one embodiment of the present invention, thewater partial pressure in said gas mixture is equal to or greater thanabout 0.4 bar. In another embodiment of the present invention, the waterpartial pressure in said gas mixture is equal to or greater than about0.8 bar. In another embodiment of the present invention, the waterpartial pressure in said gas mixture is equal to or greater than about 4bar. In another embodiment of the present invention, the water partialpressure in said gas mixture is between about 5 bar and about 35 bar. Inanother embodiment of the present invention, said contacting step isperformed under a total pressure equal to or greater than about 1 bar.In another embodiment of the present invention, said contacting step isperformed under a total pressure equal to or greater than about 4 bar.In yet another embodiment of the present invention, said contacting stepis performed under a total pressure between about 4 bar and about 35bar.

In another embodiment of the present invention, said contacting stepbetween said dehydration catalyst precursor mixture and said gas mixtureis performed at a temperature equal to or greater than about 250° C. Inanother embodiment of the present invention, said contacting stepbetween said dehydration catalyst precursor mixture and said gas mixtureis performed at a temperature between about 300° C. and about 450° C.

The method of preparing the dehydration catalyst can comprise mixing oftwo or more different materials. This mixing step can be performed byany method known to those skilled in the art, such as, by way of exampleand not limitation: solid mixing, impregnation, or co-precipitation. Inthe solid mixing method, the various components are physically mixedtogether with optional grinding using any method known to those skilledin the art, such as, by way of example and not limitation, shear,extensional, kneading, extrusion, ball milling, and others, andalternatively followed by any additional treatment or activation step.In the impregnation method, a suspension of insoluble material (e.g.inert support) is treated with a solution of catalyst solubleingredients, and the resulting material is then treated or activatedunder conditions that will convert the mixture to a more active orpreferred state. In the co-precipitation method, a homogenous solutionof the catalyst ingredients is precipitated by the addition ofadditional ingredients, followed by optional filtration and heating toremove solvents and volatile materials (e.g., water, nitric acid, carbondioxide, ammonia, or acetic acid).

Mixing of catalyst components with surfactants followed by heating canincrease catalyst surface area. In one embodiment of the presentinvention, the method of preparing the dehydration catalyst furthercomprises mixing one or more surfactants with said one or more precursorphosphate salts, said two or more different phosphate precursorcompounds, or said dehydration catalyst precursor mixture before saidcontacting step with said gas mixture. In another embodiment of thepresent invention, said one or more surfactants are cationic orzwitterionic. Non limiting examples of surfactants aremyristyltrimethylammonium bromide, hexadecyltrimethylammonium bromide,dodecyltrimethylammonium bromide, decyltrimethylammonium bromide, andoctadecyltrimethyl ammonium bromide.

Heating can promote chemical reactions, thermal decompositions, phasetransitions, and/or removal of volatile materials. In one embodiment ofthe present invention, the method of preparing the dehydration catalystfurther comprises heating said one or more precursor phosphate salts,said two or more different phosphate precursor compounds, or saiddehydration catalyst precursor mixture at a temperature equal to orgreater than 180° C. before said contacting step with said gas mixture.In another embodiment of the present invention, the method of preparingthe dehydration catalyst further comprises heating said one or moreprecursor phosphate salts, said two or more different phosphateprecursor compounds, or said dehydration catalyst precursor mixture at atemperature equal to or greater than 300° C. before said contacting stepwith said gas mixture. In another embodiment of the present invention,the method of preparing the dehydration catalyst further comprisesheating said one or more precursor phosphate salts, said two or moredifferent phosphate precursor compounds, or said dehydration catalystprecursor mixture at a temperature between about 350° C. and about 650°C. before said contacting step with said gas mixture. In anotherembodiment of the present invention, the method of preparing thedehydration catalyst further comprises heating said one or moreprecursor phosphate salts, said two or more different phosphateprecursor compounds, or said dehydration catalyst precursor mixture at atemperature between about 400° C. and about 450° C. before saidcontacting step with said gas mixture. Said heating step is typicallydone using any method known to those skilled in the art, such as, by wayof example and not limitation, convection, conduction, radiation,microwave heating, and others. The heating step is performed withequipment such as, by way of example and not limitation, furnaces,atomizers, or reactors of various designs, comprising shaft furnaces,rotary kilns, hearth furnaces, fluidized bed reactors, spay dryers. Theduration of said heating step is, in one embodiment of the presentinvention, about one hour to about seventy-two hours. In anotherembodiment, the duration of said heating step is between about two hoursand about twelve hours. In yet another embodiment, the duration of saidheating step is about four hours. In one embodiment, the temperatureramp in said heating step is between about 0.5° C./min and about 20°C./min. In another embodiment, the temperature ramp in said heating stepis about 10° C./min.

In one embodiment of the present invention, the method of preparing thedehydration catalyst further comprises molding the particles of said oneor more precursor phosphate salts, said two or more different phosphateprecursor compounds, or said dehydration catalyst precursor mixturebefore said contacting step with said gas mixture. Non limiting examplesof molding operations are granulation, agglomeration, compaction,pelleting, and extrusion. In another embodiment of the presentinvention, the method of preparing the dehydration catalyst furthercomprises size reduction or grinding of the particles of said one ormore precursor phosphate salts, said two or more different phosphateprecursor compounds, or said dehydration catalyst precursor mixturebefore said contacting step with said gas mixture. In one embodiment ofthe present invention, the method of preparing the dehydration catalystfurther comprises sieving the particles of said one or more precursorphosphate salts, said two or more different phosphate precursorcompounds, or said dehydration catalyst precursor mixture to select amaterial of specific size distribution before said contacting step withsaid gas mixture. In another embodiment of the present invention, themethod of preparing the dehydration catalyst further comprises sievingthe particles of said one or more precursor phosphate salts, said two ormore different phosphate precursor compounds, or said dehydrationcatalyst precursor mixture to a median particle size of about 50 μm toabout 500 μm. In yet another embodiment of the present invention, themethod of preparing the dehydration catalyst further comprises sievingthe particles of said one or more precursor phosphate salts, said two ormore different phosphate precursor compounds, or said dehydrationcatalyst precursor mixture to a median particle size of about 100 μm toabout 200 μm.

In another embodiment, the dehydration catalyst is prepared by thefollowing steps, which comprise: (a) mixing KH₂PO₄ and amorphous silicain a weight ratio between about 2:1 and about 1:8, to produce adehydration catalyst precursor mixture, (b) heating said dehydrationcatalyst precursor mixture between about 200° C. and about 650° C. forabout one hour to about twelve hours, to produce a calcined dehydrationcatalyst precursor mixture, (c) optionally grinding and sieving saidcalcined dehydration catalyst precursor mixture, to produce a grounddehydration catalyst precursor mixture, and (d) contacting said calcineddehydration catalyst precursor mixture or said ground dehydrationcatalyst precursor mixture with a gas mixture comprising nitrogen andwater vapor; wherein the water partial pressure in said gas mixture isbetween about 5 bar and about 15 bar and wherein said contacting step isperformed at a temperature between about 325° C. and about 425° C., toproduce said dehydration catalyst.

In another embodiment, the dehydration catalyst is prepared by thefollowing steps, which comprise: (a) mixing KH₂PO₄ and BaSO₄ in a weightratio between about 2:1 and about 1:8, to produce a dehydration catalystprecursor mixture, (b) heating said dehydration catalyst precursormixture between about 200° C. and about 650° C. for about one hour toabout twelve hours, to produce a calcined dehydration catalyst precursormixture, (c) optionally grinding and sieving said calcined dehydrationcatalyst precursor mixture, to produce a ground dehydration catalystprecursor mixture, and (d) contacting said calcined dehydration catalystprecursor mixture or said ground dehydration catalyst precursor mixturewith a gas mixture comprising nitrogen and water vapor; wherein thewater partial pressure in said gas mixture is between about 5 bar andabout 15 bar and wherein said contacting step is performed at atemperature between about 325° C. and about 425° C., to produce saiddehydration catalyst.

In another embodiment, the dehydration catalyst is prepared by thefollowing steps, which comprise: (a) mixing K₂HPO₄, (NH₄)₂HPO₄, andamorphous silica in a weight ratio between about 1.3:1.0:16.1 and about1.3:1.0:1.2, to produce a dehydration catalyst precursor mixture, (b)heating said dehydration catalyst precursor mixture between about 200°C. and about 650° C. for about one hour to about twelve hours, toproduce a calcined precursor mixture, (c) optionally grinding andsieving said calcined dehydration catalyst precursor mixture, to producea ground dehydration catalyst precursor mixture, and (d) contacting saidcalcined dehydration catalyst precursor mixture or said grounddehydration catalyst precursor mixture with a gas mixture comprisingnitrogen and water vapor; wherein the water partial pressure in said gasmixture is between about 5 bar and about 15 bar and wherein saidcontacting step is performed at a temperature between about 325° C. andabout 425° C., to produce said dehydration catalyst.

Following preparation, the catalyst can be utilized to catalyze severalchemical reactions. Non limiting examples of reactions are: dehydrationof lactic acid to acrylic acid (as described in further detail below);dehydration of 3-hydroxypropionic acid or 3-hydroxypropionic acidderivatives, or mixtures thereof to acrylic acid; dehydration ofglycerin to acrolein; isomerization of lactic acid to 3-hydroxypropionicacid in the presence of water; reduction of hydroxypropionic acid topropionic acid or 1-propanol in the presence of hydrogen gas;dehydration of aliphatic alcohols to alkenes or olefins; dehydrogenationof aliphatic alcohols to ethers; other dehydrogenations, hydrolyses,alkylations, dealkylations, oxidations, disproportionations,esterifications, cyclizations, isomerizations, condensations,aromatizations, polymerizations; and other reactions that may beapparent to those having ordinary skill in the art.

IV Methods of Producing Acrylic Acid, Acrylic Acid Derivatives, orMixtures Thereof

The inventors have unexpectedly found that the method of dehydratinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof can produce high yield to and selectivity of acrylic acid,acrylic acid derivatives, or mixtures thereof when the dehydrationcatalyst is prepared according to the present invention and thedehydration reaction is operated under a water partial pressure of morethan about 0.4 bar. Not wishing to be bound by theory, the inventorsbelieve that the elevated water partial pressure enhances the catalystactivity due to the formation (or preservation) of Brønsted acid sitesfrom less protonated catalyst precursors. Thus, the inventors have alsounexpectedly found that the process of dehydrating hydroxypropionic acidcan be more efficient in the presence of elevated water partial pressurethan under low water partial pressure or atmospheric conditions usuallypreferred in the art.

A method for dehydrating hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof to acrylic acid, acrylic acidderivatives, or mixtures thereof is provided. In one embodiment of thepresent invention, said hydroxypropionic acid is selected from the groupconsisting of lactic acid (2-hydroxypropionic), 3-hydroxypropionic acid,and mixtures thereof; and said hydroxypropionic acid derivatives areselected from the group consisting of lactic acid derivatives,3-hydroxypropionic acid derivatives, and mixtures thereof. In anotherembodiment of the present invention, said hydroxypropionic acid islactic acid and said hydroxypropionic acid derivatives are lactic acidderivatives.

Lactic acid can be D-lactic acid, L-lactic acid, or mixture thereof.Lactic acid derivatives can be metal or ammonium salts of lactic acid,alkyl esters of lactic acid, lactic acid oligomers, cyclic di-esters oflactic acid, lactic acid anhydride, 2-alkoxypropionic acids or theiralkyl esters, 2-aryloxypropionic acids or their alkyl esters,2-acyloxypropionic acids or their alkyl esters, or a mixture thereof.Non limiting examples of metal salts of lactic acid are sodium lactate,potassium lactate, and calcium lactate. Non limiting examples of alkylesters of lactic acid are methyl lactate, ethyl lactate, butyl lactate,2-ethylhexyl lactate, and mixtures thereof. A non limiting example ofcyclic di-esters of lactic acid is dilactide. Non limiting examples of2-alkoxypropionic acids are 2-methoxypropionic acid and2-ethoxypropionic acid. A non limiting example of 2-aryloxypropionicacid is 2-phenoxypropionic acid. A non limiting example of2-acyloxypropionic acid is 2-acetoxypropionic acid. In one embodiment ofthe present invention, the lactic acid derivative is methyl lactate.Methyl lactate can be neat or in a solution with water, methanol, ormixtures thereof.

3-hydroxypropionic acid derivatives can be metal or ammonium salts of3-hydroxypropionic acid, alkyl esters of 3-hydroxypropionic acid,3-hydroxypropionic acid oligomers, 3-alkoxypropionic acids or theiralkyl esters, 3-aryloxypropionic acids or their alkyl esters,3-acyloxypropionic acids or their alkyl esters, or a mixture thereof.Non limiting examples of metal salts of 3-hydroxypropionic acid aresodium 3-hydroxypropionate, potassium 3-hydroxypropionate, and calcium3-hydroxypropionate. Non limiting examples of alkyl esters ofhydroxypropionic acid are methyl 3-hydroxypropionate, ethyl3-hydroxypropionate, butyl 3-hydroxypropionate, 2-ethylhexyl3-hydroxypropionate, and mixtures thereof. Non limiting examples of3-alkoxypropionic acids are 3-methoxypropionic acid and3-ethoxypropionic acid. A non limiting example of 3-aryloxypropionicacid is 3-phenoxypropionic acid. A non limiting example of3-acyloxypropionic acid is 3-acetoxypropionic acid.

Acrylic acid derivatives can be metal or ammonium salts of acrylic acid,alkyl esters of acrylic acid, acrylic acid oligomers, or mixturesthereof. Non limiting examples of metal salts of acrylic acid are sodiumacrylate, potassium acrylate, and calcium acrylate. Non limitingexamples of alkyl esters of acrylic acid are methyl acrylate, ethylacrylate, butyl acrylate, 2-ethylhexyl acrylate, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprisescontacting: a) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; b) water vapor; and c) any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step is equalto or greater than the water partial pressure at the triple point of atleast one of said one or more amorphous phosphate salts or said one ormore precursor phosphate salts in said dehydration catalyst or saiddehydration catalyst precursor mixture; wherein said contacting step isperformed at a temperature equal to or greater than the temperature atthe triple point of at least one of said one or more amorphous phosphatesalts or said one or more precursor phosphate salts in said dehydrationcatalyst or said dehydration catalyst precursor mixture; and wherebysaid acrylic acid, acrylic acid derivatives, or mixtures thereof isproduced as a result of said water vapor and said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof being contactedwith said dehydration catalyst or said dehydration catalyst precursormixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprisescontacting: a) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; b) water vapor; and c) any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step is equalto or greater than about 4 bar; wherein said contacting step isperformed at a temperature equal to or greater than about 250° C.; andwhereby said acrylic acid, acrylic acid derivatives, or mixtures thereofis produced as a result of said water vapor and said hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof beingcontacted with said dehydration catalyst or said dehydration catalystprecursor mixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprisescontacting: a) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; b) water vapor; and c) any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention,wherein said one or more monovalent cations are selected from the groupconsisting of Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof; wherein the waterpartial pressure during said contacting step is equal to or greater thanabout 0.8 bar; wherein said contacting step is performed at atemperature equal to or greater than about 250° C.; and whereby saidacrylic acid, acrylic acid derivatives, or mixtures thereof is producedas a result of said water vapor and said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof being contactedwith said dehydration catalyst or said dehydration catalyst precursormixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprisescontacting: a) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; b) water vapor; c) an essentially chemically inertgas or essentially chemically inert liquid; and d) any dehydrationcatalyst disclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step is equalto or greater than the water partial pressure at the triple point of atleast one of said one or more amorphous phosphate salts or said one ormore precursor phosphate salts in said dehydration catalyst or saiddehydration catalyst precursor mixture; wherein said contacting step isperformed at a temperature equal to or greater than the temperature atthe triple point of at least one of said one or more amorphous phosphatesalts or said one or more precursor phosphate salts in said dehydrationcatalyst or said dehydration catalyst precursor mixture; and wherebysaid acrylic acid, acrylic acid derivatives, or mixtures thereof isproduced as a result of said water vapor and said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof being contactedwith said dehydration catalyst or said dehydration catalyst precursormixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprisescontacting: a) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; b) water vapor; c) an essentially chemically inertgas or essentially chemically inert liquid; and d) any dehydrationcatalyst disclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step is equalto or greater than about 4 bar; wherein said contacting step isperformed at a temperature equal to or greater than about 250° C.; andwhereby said acrylic acid, acrylic acid derivatives, or mixtures thereofis produced as a result of said water vapor and said hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof beingcontacted with said dehydration catalyst or said dehydration catalystprecursor mixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprisescontacting: a) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; b) water vapor; c) an essentially chemically inertgas or essentially chemically inert liquid; and d) any dehydrationcatalyst disclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention,wherein said one or more monovalent cations are selected from the groupconsisting of Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof; wherein the waterpartial pressure during said contacting step is equal to or greater thanabout 0.8 bar; wherein said contacting step is performed at atemperature equal to or greater than about 250° C.; and whereby saidacrylic acid, acrylic acid derivatives, or mixtures thereof is producedas a result of said water vapor and said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof being contactedwith said dehydration catalyst or said dehydration catalyst precursormixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In one embodiment of the present invention, said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof are in the gasphase, at least partially, during said contacting step with saiddehydration catalyst or said dehydration catalyst precursor mixture. Inanother embodiment of the present invention, said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof are in the liquidphase, at least partially, during said contacting step with saiddehydration catalyst or said dehydration catalyst precursor mixture.

In one embodiment of the present invention, a method of making acrylicacid is provided. The method comprises contacting: (a) a gas mixturecomprising: i) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; and ii) water vapor; with (b) any dehydrationcatalyst disclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than the water partial pressure atthe triple point of at least one of said one or more amorphous phosphatesalts or said one or more precursor phosphate salts in said dehydrationcatalyst or said dehydration catalyst precursor mixture; wherein saidcontacting step is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate saltsin said dehydration catalyst or said dehydration catalyst precursormixture; and whereby said acrylic acid, acrylic acid derivatives, ormixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst or saiddehydration catalyst precursor mixture. In another embodiment of thepresent invention, said hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said method of making acrylic acid,acrylic acid derivatives, or mixtures thereof are lactic acid, lacticacid derivatives, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid is provided. The method comprises contacting: (a) a gas mixturecomprising: i) hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof; and ii) water vapor; with (b) any dehydrationcatalyst disclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than about 4 bar; wherein saidcontacting step is performed at a temperature equal to or greater thanabout 250° C.; and whereby said acrylic acid, acrylic acid derivatives,or mixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst or saiddehydration catalyst precursor mixture. In another embodiment of thepresent invention, said hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said method of making acrylic acid,acrylic acid derivatives, or mixtures thereof are lactic acid, lacticacid derivatives, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprisescontacting: (a) a gas mixture comprising: i) hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; and ii) watervapor; with (b) any dehydration catalyst disclosed in Section II(“Catalysts for the Conversion of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) of the present invention, wherein said one or moremonovalent cations are selected from the group consisting of Na⁺, K⁺,Rb⁺, Cs⁺, and mixtures thereof; wherein the water partial pressureduring said contacting step in said gas mixture is equal to or greaterthan about 0.8 bar; wherein said contacting step is performed at atemperature equal to or greater than about 250° C.; and whereby saidacrylic acid, acrylic acid derivatives, or mixtures thereof is producedas a result of said water vapor and said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof being contactedwith said dehydration catalyst or said dehydration catalyst precursormixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprisescontacting: (a) a liquid mixture comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; and (b) a gasmixture comprising water vapor; with (c) any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than the water partial pressure atthe triple point of at least one of said one or more amorphous phosphatesalts or said one or more precursor phosphate salts in said dehydrationcatalyst or said dehydration catalyst precursor mixture; wherein saidcontacting step is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate saltsin said dehydration catalyst or said dehydration catalyst precursormixture; and whereby said acrylic acid, acrylic acid derivatives, ormixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst or saiddehydration catalyst precursor mixture. In another embodiment of thepresent invention, said hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said method of making acrylic acid,acrylic acid derivatives, or mixtures thereof are lactic acid, lacticacid derivatives, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprisescontacting: (a) a liquid mixture comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; and (b) a gasmixture comprising water vapor; with (c) any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention;wherein the water partial pressure during said contacting step in saidgas mixture is equal to or greater than about 4 bar; wherein saidcontacting step is performed at a temperature equal to or greater thanabout 250° C.; and whereby said acrylic acid, acrylic acid derivatives,or mixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst or saiddehydration catalyst precursor mixture. In another embodiment of thepresent invention, said hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said method of making acrylic acid,acrylic acid derivatives, or mixtures thereof are lactic acid, lacticacid derivatives, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprisescontacting: (a) a liquid mixture comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; and (b) a gasmixture comprising water vapor; with (c) any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) of the present invention,wherein said one or more monovalent cations are selected from the groupconsisting of Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof; wherein the waterpartial pressure during said contacting step in said gas mixture isequal to or greater than about 0.8 bar; wherein said contacting step isperformed at a temperature equal to or greater than about 250° C.; andwhereby said acrylic acid, acrylic acid derivatives, or mixtures thereofis produced as a result of said water vapor and said hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof beingcontacted with said dehydration catalyst or said dehydration catalystprecursor mixture. In another embodiment of the present invention, saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said method of making acrylic acid, acrylic acid derivatives,or mixtures thereof are lactic acid, lactic acid derivatives, ormixtures thereof.

In another embodiment of the present invention, said gas mixture furthercomprises an essentially chemically inert gas. In the context of thepresent invention, an essentially chemically inert gas is any gas thatis essentially chemically inert to said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof, but notnecessarily to said dehydration catalyst or said dehydration catalystprecursor mixture. Non limiting examples of essentially chemically inertgases are nitrogen, helium, argon, carbon dioxide, carbon monoxide, air,water vapor, and mixtures thereof. In another embodiment of the presentinvention, said essentially chemically inert gas comprises nitrogen. Inyet another embodiment of the present invention, said essentiallychemically inert gas consists essentially of nitrogen.

In another embodiment, said liquid mixture comprising hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof can furthercomprise one or more essentially chemically inert liquids. Non limitingexamples of essentially chemically inert liquids are water,hydrocarbons, chlorinated hydrocarbons, fluorinated hydrocarbons,brominated hydrocarbons, esters, ethers, ketones, aldehydes, acids,alcohols, or mixtures thereof. Non limiting examples of hydrocarbons areC5 to C8 linear and branched alkanes. A non limiting example of estersis ethyl acetate. A non limiting example of ethers is diphenyl ether. Anon limiting example of ketones is acetone. Non limiting examples ofalcohols are methanol, ethanol, and C3 to C8 linear and branchedalcohols. In one embodiment of the present invention, said one or moreessentially chemically inert liquids comprise water. In one embodimentof the present invention, said one or more essentially chemically inertliquids consists essentially of water.

In one embodiment of the present invention, a liquid mixture comprisinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof is fed into an evaporator upstream of the catalytic reactor forthe liquid mixture to become a gas mixture, at least partially, beforecontacting said dehydration catalyst or said dehydration catalystprecursor mixture. In another embodiment of the present invention, aliquid mixture comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof is fed directly into the catalyticreactor and contacted with said dehydration catalyst or said dehydrationcatalyst precursor mixture. In another embodiment of the presentinvention, an essentially chemically inert gas or an essentiallychemically inert liquid is fed into the evaporator or into the catalyticreactor. The liquid mixture comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof and theessentially chemically inert gas or the essentially chemically inertliquid can be jointly or separately fed into said evaporator or saidcatalytic reactor. Non limiting examples of essentially chemically inertgases are nitrogen, helium, air, argon, carbon dioxide, carbon monoxide,water vapor, and mixtures thereof. Non limiting examples of essentiallychemically inert liquids are water, hydrocarbons, chlorinatedhydrocarbons, fluorinated hydrocarbons, brominated hydrocarbons, esters,ethers, ketones, aldehydes, acids, alcohols, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises: a)providing a liquid mixture comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; b) optionallycombining said liquid mixture with an essentially chemically inert gasto form a liquid/gas blend; and c) contacting said liquid mixture orsaid liquid/gas blend with any dehydration catalyst disclosed in SectionII (“Catalysts for the Conversion of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) under a water partial pressure of about 0.4 bar ormore to produce an acrylic acid mixture comprising said acrylic acid,acrylic acid derivatives, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises: a)providing a liquid mixture comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; b) optionally combining said liquid mixture with an essentiallychemically inert gas to form a liquid/gas blend; and c) contacting saidliquid mixture or said liquid/gas blend with any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) under a water partialpressure of about 0.4 bar or more to produce an acrylic acid mixturecomprising said acrylic acid, acrylic acid derivatives, or mixturesthereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises: a)providing a liquid mixture comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; b) optionally combining said liquid mixture with an essentiallychemically inert gas to form a liquid/gas blend; c) evaporating saidliquid mixture or said liquid/gas blend to produce a gas mixture; and d)contacting said gas mixture with any dehydration catalyst disclosed inSection II (“Catalysts for the Conversion of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) under a water partial pressure of about 0.4 bar ormore to produce an acrylic acid mixture comprising said acrylic acid,acrylic acid derivatives, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises: a)providing a liquid mixture comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof, wherein the hydroxypropionic acid is essentially in monomericform in the aqueous solution; b) optionally combining said liquidmixture with an essentially chemically inert gas to form a liquid/gasblend; c) evaporating said liquid mixture or said liquid/gas blend toproduce a gas mixture; and d) contacting said gas mixture with anydehydration catalyst disclosed in Section II (“Catalysts for theConversion of Hydroxypropionic Acid or its Derivatives to Acrylic Acidor its Derivatives”) or any dehydration catalyst precursor mixturedisclosed in Section III (“Catalyst Preparation Method”) under a waterpartial pressure of about 0.4 bar or more to produce an acrylic acidmixture comprising said acrylic acid, acrylic acid derivatives, ormixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing a liquid mixture comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof, wherein the hydroxypropionic acid is essentially in monomericform in the aqueous solution, and wherein the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof comprise betweenabout 10 wt % and about 25 wt % of the aqueous solution; b) optionallycombining said liquid mixture with an essentially chemically inert gasto form a liquid/gas blend; c) evaporating said liquid mixture or saidliquid/gas blend to produce a gas mixture; and d) contacting said gasmixture with any dehydration catalyst disclosed in Section II(“Catalysts for the Conversion of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) under a water partial pressure of about 0.4 bar ormore to produce an acrylic acid mixture comprising said acrylic acid,acrylic acid derivatives, or mixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing a liquid mixture comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof, wherein the hydroxypropionic acid comprises oligomers in theaqueous solution; b) heating said liquid mixture at a temperaturebetween about 50° C. and about 100° C. to hydrolyze the oligomers of thehydroxypropionic acid and produce a liquid mixture comprising monomerichydroxypropionic acid; c) optionally combining said liquid mixturecomprising monomeric hydroxypropionic acid with an essentiallychemically inert gas to form a liquid/gas blend; d) evaporating saidliquid mixture comprising monomeric hydroxypropionic acid or saidliquid/gas blend to produce a gas mixture; and e) contacting said gasmixture with any dehydration catalyst disclosed in Section II(“Catalysts for the Conversion of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) under a water partial pressure of about 0.4 bar ormore to produce an acrylic acid mixture comprising said acrylic acid,acrylic acid derivatives, or mixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing a liquid mixture comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; b) optionally combining the liquid mixture with an essentiallychemically inert gas to form a liquid/gas blend; c) evaporating saidliquid mixture or said liquid/gas blend to produce a gas mixture; d)contacting said gas mixture with any dehydration catalyst disclosed inSection II (“Catalysts for the Conversion of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) under a water partial pressure of about 0.4 bar ormore to produce an acrylic acid mixture comprising acrylic acid, acrylicacid derivatives, or mixtures thereof; and e) cooling said acrylic acidmixture to produce a liquid acrylic acid composition comprising acrylicacid, acrylic acid derivatives, or mixtures thereof.

In one embodiment of the present invention, the concentration of thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said liquid mixture is between about 2 wt % and about 95 wt%. In another embodiment of the present invention, the concentration ofthe hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof in said liquid mixture is between about 5 wt % andabout 60 wt %. In another embodiment of the present invention, theconcentration of the hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said liquid mixture is between about10 wt % and about 40 wt %. In yet another embodiment of the presentinvention, the concentration of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof in said liquidmixture is about 20 wt %.

In one embodiment of the present invention, the liquid mixture comprisesan aqueous solution of hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof. In another embodiment of the presentinvention, the liquid mixture comprises an aqueous solution of lacticacid, lactic acid derivatives, or mixtures thereof. In anotherembodiment of the present invention, said lactic acid derivatives insaid aqueous solution are selected from the group consisting of metal orammonium salts of lactic acid, alkyl esters of lactic acid, lactic acidoligomers, cyclic di-esters of lactic acid, lactic acid anhydride,2-alkoxypropionic acids or their alkyl esters, 2-aryloxypropionic acidsor their alkyl esters, 2-acyloxypropionic acids or their alkyl esters,or a mixture thereof.

In one embodiment of the present invention, the concentration of thelactic acid, lactic acid derivatives, or mixtures thereof in saidaqueous solution is between about 2 wt % and about 95 wt %. In anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said aqueoussolution is between about 5 wt % and about 60 wt %. In anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said aqueoussolution is between about 10 wt % and about 40 wt %. In anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said aqueoussolution is about 20 wt %. In another embodiment of the presentinvention, the liquid mixture comprises an aqueous solution of lacticacid along with lactic acid derivatives. In another embodiment of thepresent invention, the liquid mixture comprises less than about 30 wt %of lactic acid derivatives, based on the total weight of the liquidmixture. In another embodiment of the present invention, the liquidmixture comprises less than about 10 wt % of lactic acid derivatives,based on the total weight of the liquid mixture. In yet anotherembodiment of the present invention, the liquid mixture comprises lessthan about 5 wt % of lactic acid derivatives, based on the total weightof the liquid mixture.

Lactic acid can be in monomeric form or as oligomers in said aqueoussolution of lactic acid, lactic acid derivatives, or mixtures thereof.In one embodiment of the present invention, the oligomers of the lacticacid in said aqueous solution of lactic acid, lactic acid derivatives,or mixtures thereof are less than about 30 wt % based on the totalamount of lactic acid, lactic acid derivatives, or mixtures thereof. Inanother embodiment of the present invention, the oligomers of the lacticacid in said aqueous solution of lactic acid, lactic acid derivatives,or mixtures thereof are less than about 10 wt % based on the totalamount of lactic acid, lactic acid derivatives, or mixtures thereof. Inanother embodiment of the present invention, the oligomers of the lacticacid in said aqueous solution of lactic acid, lactic acid derivatives,or mixtures thereof are less than about 5 wt % based on the total amountof lactic acid, lactic acid derivatives, or mixtures thereof. In yetanother embodiment of the present invention, the lactic acid isessentially in monomeric form in said aqueous solution of lactic acid,lactic acid derivatives, or mixtures thereof.

The process to remove the oligomers from the aqueous solution of lacticacid, lactic acid derivatives, and mixtures thereof can comprise apurification step or hydrolysis by heating step. In one embodiment ofthe present invention, the heating step can involve heating the aqueoussolution of lactic acid, lactic acid derivatives, or mixtures thereof ata temperature between about 50° C. and about 100° C. to hydrolyze theoligomers of the lactic acid. In another embodiment of the presentinvention, the heating step can involve heating the aqueous solution oflactic acid, lactic acid derivatives, or mixtures thereof at atemperature between about 95° C. and about 100° C. to hydrolyze theoligomers of the lactic acid. In another embodiment of the presentinvention, the heating step can involve heating the aqueous solution oflactic acid, lactic acid derivatives, or mixtures thereof at atemperature between about 50° C. and about 100° C. to hydrolyze theoligomers of the lactic acid and produce a monomeric lactic acid aqueoussolution comprising at least 80 wt % of lactic acid in monomeric formbased on the total amount of lactic acid, lactic acid derivatives, ormixtures thereof. In another embodiment of the present invention, theheating step can involve heating the aqueous solution of lactic acid,lactic acid derivatives, or mixtures thereof at a temperature betweenabout 50° C. and about 100° C. to hydrolyze the oligomers of the lacticacid and produce a monomeric lactic acid aqueous solution comprising atleast 95 wt % of lactic acid in monomeric form based on the total amountof lactic acid, lactic acid derivatives, or mixtures thereof. In anotherembodiment of the present invention, an about 88 wt % aqueous solutionof lactic acid, lactic acid derivatives, or mixtures thereof is dilutedwith water and the oligomers are hydrolyzed to produce an aqueoussolution of about 20 wt % lactic acid. The lactic acid oligomers canresult in loss of acrylic acid selectivity due to their high boilingpoint. As the water content decreases in the aqueous solution, the lossof feed material to the catalyst reaction, due to losses in theevaporating step, increases. Additionally, lactic acid oligomers cancause coking, catalyst deactivation, and reactor plugging.

In another embodiment of the present invention, the liquid mixturecomprising hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof can further comprise one or more antioxidants. Inanother embodiment of the present invention, the liquid mixturecomprising hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof further comprises butylated hydroxy toluene (BHT),butylated hydroxy anisole (BHA), or mixtures thereof. In yet anotherembodiment of the present invention, the liquid mixture comprisinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof further comprises ethylene glycol, ethanedithiol, methanol,methanethiol, or mixtures thereof.

The liquid mixture can be introduced into the evaporator or into thecatalytic reactor with a simple tube or through atomization nozzles. Nonlimiting examples of atomization nozzles comprise fan nozzles, pressureswirl atomizers, air blast atomizers, two-fluid atomizers, rotaryatomizers, and supercritical carbon dioxide atomizers. In one embodimentof the present invention, the droplets of the aqueous solution are lessthan about 500 μm in diameter. In another embodiment of the presentinvention, the droplets of the aqueous solution are less than about 200μm in diameter. In yet another embodiment of the present invention, thedroplets of the aqueous solution are less than about 100 μm in diameter.

In the evaporating step, said liquid mixture or said liquid/gas blendare heated to produce a gas mixture. In one embodiment of the presentinvention, the temperature during the evaporating step is between about165° C. and about 450° C. In another embodiment of the presentinvention, the temperature during the evaporating step is between about200° C. and about 400° C. In another embodiment of the presentinvention, the temperature during the evaporating step is between about250° C. and about 375° C. In one embodiment of the present invention,the residence time in the evaporator during said evaporating step isbetween about 0.5 s and about 10 s. In another embodiment of the presentinvention, the residence time in the evaporator during said evaporatingstep is between about 1 s and about 5 s.

The evaporating step can be performed under vacuum, at atmosphericpressure, or at higher than atmospheric pressure. In one embodiment ofthe present invention, the evaporating step is performed under a totalpressure of at least about 1 bar. In another embodiment of the presentinvention, the evaporating step is performed under a total pressurebetween about 5 bar and about 40 bar. In yet another embodiment of thepresent invention, the evaporating step is performed under a pressurebetween about 10 bar and about 35 bar. In yet another embodiment of thepresent invention, the evaporating step is performed under a totalpressure of about 25 bar.

The evaporating step can be performed in various types of evaporators,such as, but not limited to, atomizer, plate heat exchanger, empty flowreactor, and fixed bed flow reactor. The evaporating step can beperformed in an evaporator with the liquid mixture flowing down, orflowing up, or flowing horizontally. In one embodiment of the presentinvention, the evaporating step is performed in an evaporator with theliquid flowing down. Also, the evaporating step can be done in a batchform.

In one embodiment of the present invention, the material of theevaporator interior surface is selected from the group consisting ofamorphous silica, quartz, other silicon oxides, borosilicate glass,silicon, and mixtures thereof. In yet another embodiment of the presentinvention, the material of the evaporator interior surface is amorphoussilica or borosilicate glass.

In one embodiment of the present invention, the evaporating andcontacting steps are combined in a single step. In another embodiment ofthe present invention, the evaporating and contacting steps areperformed sequentially in a single reactor. In yet another embodiment ofthe present invention, the evaporating and contacting steps areperformed sequentially in a tandem reactor.

The gas mixture comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof or the liquid mixture comprisinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof are converted to acrylic acid, acrylic acid derivatives, andmixture thereof by contacting said mixtures with a dehydration catalystor a dehydration catalyst precursor mixture. The dehydration catalystcan be selected from the group comprising phosphates, sulfates,tantalates, metal oxides, aluminates, silicates, aluminosilicates (e.g.,zeolites), arsenates, nitrates, vanadates, niobates, selenates,arsenatophosphates, phosphoaluminates, phosphoborates, phosphochromates,phosphomolybdates, phosphosilicates, phosphosulfates, phosphotungstates,and mixtures thereof, and others that may be apparent to those havingordinary skill in the art. The dehydration catalyst can contain one ormore inert supports. Non limiting examples of inert supports are silicaor silicates, alumina or aluminates, aluminosilicates, titania ortitanates, zirconia or zirconates, carbons (such as activated carbon,diamond, graphite, or fullerenes), sulfates, phosphates, tantalates,ceria, other metal oxides, and mixtures thereof. In one embodiment ofthe present invention, the dehydration catalyst is any dehydrationcatalyst disclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”).

In the context of the present invention, “contacting” refers to theaction of bringing said hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in close proximity to the surface ofsaid dehydration catalyst or dehydration catalyst precursor mixture. Thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof must contact the surface of the dehydration catalyst or thedehydration catalyst precursor mixture at a rate that is slow enough forthe dehydration reaction to occur, yet fast enough to avoid thedegradation of hydroxypropionic acid, acrylic acid, or their derivativesto undesirable products at the temperature of said contacting step.Several parameters can be used to describe the rate of said contactingstep, such as, by way of example and not limitation, WHSV, GHSV, LHSV,and weight velocity per unit of accessible catalyst surface area (WVSA)that can be calculated as the ratio of WHSV and the dehydration catalystspecific surface area (SA), (WVSA=WHSV/SA); with units: g/m²·h, where grefer to g of hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof. A number of methods, based on the adsorption of aninert gas, can be used to determine the accessible surface area,including, but not limited to, the static volumentric and gravimetricmethods and the dynamic method that are well-known by those skilled inthe art.

In one embodiment of the present invention, the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof contact thedehydration catalyst or the dehydration catalyst precursor mixture at aWVSA between about 10⁴ g·m⁻²·h⁻¹ and about 10⁻⁴ g·m⁻²·h⁻¹. In anotherembodiment of the present invention, the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof contact thedehydration catalyst or the dehydration catalyst precursor mixture at aWVSA between about 10² g·m⁻²·h⁻¹ and about 10⁻² g·m⁻²·h⁻¹. In anotherembodiment of the present invention, the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof contact thedehydration catalyst or the dehydration catalyst precursor mixture at aWVSA between about 10 g·m⁻²·h⁻¹ and about 0.1 g·m⁻²·h⁻¹.

In one embodiment of the present invention, the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof contact thedehydration catalyst or the dehydration catalyst precursor mixture at aWHSV between about 0.02 h⁻¹ and about 10 h⁻¹. In another embodiment ofthe present invention, the hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof contact the dehydration catalyst or thedehydration catalyst precursor mixture at a WHSV between about 0.2 h⁻¹and about 1 h⁻¹. In another embodiment of the present invention, thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof contact the dehydration catalyst or the dehydration catalystprecursor mixture at a WHSV between about 0.4 h⁻¹ and about 0.7 h⁻¹. Inanother embodiment of the present invention, the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof contact thedehydration catalyst or the dehydration catalyst precursor mixture at aWHSV of about 0.5 h⁻¹.

When hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof are in the gas phase during said contacting step withsaid dehydration catalyst or said dehydration catalyst precursormixture, and in another embodiment of the present invention, the gasmixture comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof contacts the dehydration catalyst orthe dehydration catalyst precursor mixture at a GHSV between about 720h⁻¹ and about 36,000 h⁻¹. In another embodiment of the presentinvention, the gas mixture comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof contacts thedehydration catalyst or the dehydration catalyst precursor mixture at aGHSV between about 1,800 h⁻¹ and about 9,000 h⁻¹. In another embodimentof the present invention, the gas mixture comprising hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof contactsthe dehydration catalyst or the dehydration catalyst precursor mixtureat a GHSV between about 3,600 h⁻¹ and about 6,000 h⁻¹. In anotherembodiment of the present invention, a gas mixture comprisinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof contacts the dehydration catalyst or the dehydration catalystprecursor mixture at a GHSV of about 4,500 h⁻¹.

When hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof are in the gas phase during said contacting step withsaid dehydration catalyst or said dehydration catalyst precursormixture, and in one embodiment of the present invention, theconcentration of hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof before the dehydration reaction andbased on the total moles in the gas mixture (calculated under STPconditions) is between about 0.5 mol % and about 50 mol %. In anotherembodiment of the present invention, the concentration ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof before the dehydration reaction and based on the total moles inthe gas mixture (calculated under STP conditions) is between about 1 mol% and about 10 mol %. In another embodiment of the present invention,the concentration of hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof before the dehydration reaction andbased on the total moles in the gas mixture (calculated under STPconditions) is between about 1.5 mol % and about 3.5 mol %. In yetanother embodiment of the present invention, the concentration ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof before the dehydration reaction and based on the total moles inthe gas mixture (calculated under STP conditions) is about 2.5 mol %.

In one embodiment of the present invention, the temperature during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is greater than about 150° C. In anotherembodiment of the present invention, the temperature during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is greater than about 250° C. In anotherembodiment of the present invention, the temperature during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is between about 300° C. and about 500° C. Inanother embodiment of the present invention, the temperature during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is between about 325° C. and about 400° C. Inyet another embodiment of the present invention, the temperature duringsaid contacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is between about 350° C. and about 375° C.

In one embodiment of the present invention, the temperature during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is equal to or greater than the temperatureat the triple point of at least one of said one or more amorphousphosphate salts or said one or more precursor phosphate salts. Inanother embodiment of the present invention, the temperature during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is equal to or greater than the lowest triplepoint temperature of said one or more amorphous phosphate salts or saidone or more precursor phosphate salts. In another embodiment of thepresent invention, the temperature during said contacting step with thedehydration catalyst or the dehydration catalyst precursor mixture isequal to or greater than the highest triple point temperature of saidone or more amorphous phosphate salts or said one or more precursorphosphate salts. In another embodiment of the present invention, thetemperature during said contacting step with the dehydration catalyst orthe dehydration catalyst precursor mixture is equal to or greater thanthe average temperature between the lowest triple point temperature andthe highest triple point temperature of said one or more amorphousphosphate salts or said one or more precursor phosphate salts. Inanother embodiment of the present invention, the temperature during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is at least 10° C. greater than thetemperature at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate salts.In another embodiment of the present invention, the temperature duringsaid contacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is at least 50° C. greater than thetemperature at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate salts.In another embodiment of the present invention, the temperature duringsaid contacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is at least 100° C. greater than thetemperature at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate salts.

In another embodiment of the present invention, said water partialpressure during said contacting step with the dehydration catalyst orthe dehydration catalyst precursor mixture is equal to or greater thanabout 0.4 bar. In another embodiment of the present invention, saidwater partial pressure during said contacting step with the dehydrationcatalyst or the dehydration catalyst precursor mixture is equal to orgreater than about 0.8 bar. In another embodiment of the presentinvention, said water partial pressure during said contacting step withthe dehydration catalyst or the dehydration catalyst precursor mixtureis equal to or greater than about 4 bar. In another embodiment of thepresent invention, said water partial pressure during said contactingstep with the dehydration catalyst or the dehydration catalyst precursormixture is between about 5 bar and about 35 bar.

In one embodiment of the present invention, the water partial pressureduring said contacting step with the dehydration catalyst or thedehydration catalyst precursor mixture is equal to or greater than thewater partial pressure at the triple point of at least one of said oneor more amorphous phosphate salts or said one or more precursorphosphate salts. In another embodiment of the present invention, thewater partial pressure during said contacting step with the dehydrationcatalyst or the dehydration catalyst precursor mixture is equal to orgreater than the lowest triple point water partial pressure of said oneor more amorphous phosphate salts or said one or more precursorphosphate salts. In another embodiment of the present invention, thewater partial pressure during said contacting step with the dehydrationcatalyst or the dehydration catalyst precursor mixture is equal to orgreater than the highest triple point water partial pressure of said oneor more amorphous phosphate salts or said one or more precursorphosphate salts. In another embodiment of the present invention, thewater partial pressure during said contacting step with the dehydrationcatalyst or the dehydration catalyst precursor mixture is equal to orgreater than the average water partial pressure between the lowesttriple point water partial pressure and the highest triple point waterpartial pressure of said one or more amorphous phosphate salts or saidone or more precursor phosphate salts. In one embodiment of the presentinvention, the water partial pressure during said contacting step withthe dehydration catalyst or the dehydration catalyst precursor mixtureis at least 1 bar greater than the water partial pressure at the triplepoint of at least one of said one or more amorphous phosphate salts orsaid one or more precursor phosphate salts. In one embodiment of thepresent invention, the water partial pressure during said contactingstep with the dehydration catalyst or the dehydration catalyst precursormixture is at least 2 bar greater than the water partial pressure at thetriple point of at least one of said one or more amorphous phosphatesalts or said one or more precursor phosphate salts. In one embodimentof the present invention, the water partial pressure during saidcontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is at least 5 bar greater than the waterpartial pressure at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate salts.

The contacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture can be performed under vacuum, at atmosphericpressure, or at higher than atmospheric pressure. In one embodiment ofthe present invention, the contacting step with the dehydration catalystor the dehydration catalyst precursor mixture is performed under a totalpressure of at least about 1 bar. In another embodiment of the presentinvention, the contacting step with the dehydration catalyst or thedehydration catalyst precursor mixture is performed under a totalpressure between about 5 bar and about 40 bar. In another embodiment ofthe present invention, the contacting step with the dehydration catalystor the dehydration catalyst precursor mixture is performed under a totalpressure between about 10 bar and about 35 bar. In yet anotherembodiment of the present invention, the contacting step with thedehydration catalyst or the dehydration catalyst precursor mixture isperformed under a total pressure of about 25 bar.

When hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof are in the gas phase, and in another embodiment of thepresent invention, the contacting step with the dehydration catalyst orthe dehydration catalyst precursor mixture is performed in a catalyticreactor with the gas mixture flowing down, flowing up, or flowinghorizontally. In another embodiment of the present invention, thecontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is performed in a catalytic reactor with thegas mixture flowing down. Also, the contacting step with the dehydrationcatalyst or the dehydration catalyst precursor mixture can be done in abatch form. In another embodiment of the present invention, thedehydration catalyst or the dehydration catalyst precursor mixture issuspended in an essentially chemically inert liquid. The contacting stepwith the dehydration catalyst or the dehydration catalyst precursormixture can be performed by using different catalytic reactors known tothose skilled in the art, such as, by way of example and not limitation,static reactor, stirred reactor, recirculation reactor, packed-bed flowreactor, and combinations thereof.

In one embodiment of the present invention, the contacting step with thedehydration catalyst or the dehydration catalyst precursor mixture iscarried out in an apparatus, which is pressurized to ensure that allmajor components are in the liquid phase. In another embodiment of thepresent invention, the contacting step with the dehydration catalyst orthe dehydration catalyst precursor mixture is carried out in anapparatus, which is operated at low temperature to ensure that all majorcomponents are in the liquid phase. In yet another embodiment of thepresent invention, the liquid mixture comprises an essentiallychemically inert liquid. When all major components are in the liquidphase, the contacting step with the dehydration catalyst or thedehydration catalyst precursor mixture can be performed by usingdifferent catalytic reactors, known to those skilled in the art, suchas, by way of example and not limitation, static reactor, fixed bedreactor, single-stage stirred tank reactor, multi-stage stirred tankreactor, multi-stage distillation column, and combinations thereof. Thecontacting step can be conducted batch-wise or continuously. Thecontacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture can be performed in a catalytic reactor withthe liquid mixture comprising hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof flowing down, flowing up, orflowing horizontally. In another embodiment of the present invention,the contacting step with the dehydration catalyst or the dehydrationcatalyst precursor mixture is performed in a catalytic reactor with theliquid mixture comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof flowing up.

In one embodiment of the present invention, the dehydration orisomerizations reactions of hydroxypropionic acid, hydroxypropionic acidderivatives or mixtures thereof occur in the aqueous phase, at leastpartially, and the pH of the reaction is between about 3 and about 8. Inanother embodiment of the present invention, the pH of the reaction inthe aqueous phase is between about 4 and about 7. In yet anotherembodiment of the present invention, the pH of the reaction in theaqueous phase is between about 5 and about 6.

In one embodiment of the present invention, hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof and water vaporcontact the dehydration catalyst or the dehydration catalyst precursormixture in a catalytic reactor with an interior surface materialselected from the group consisting of amorphous silica, quartz, othersilicon oxides, borosilicate glass, silicon, and mixtures thereof. Inanother embodiment of the present invention, hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof and water vaporcontact the dehydration catalyst or the dehydration catalyst precursormixture in a catalytic reactor with an interior surface materialselected from the group consisting of amorphous silica, quartz,borosilicate glass, and mixtures thereof. In another embodiment of thepresent invention, hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof and water vapor contact the dehydrationcatalyst or the dehydration catalyst precursor mixture in a catalyticreactor with an interior surface material consisting essentially ofborosilicate glass.

The acrylic acid mixture comprising acrylic acid, acrylic acidderivatives, or mixtures thereof produced in said contacting step withthe dehydration catalyst or the dehydration catalyst precursor mixtureis cooled to give a liquid acrylic acid composition as the productstream. The time required to cool the acrylic acid mixture must becontrolled to reduce acrylic acid polymerization or decomposition toethylene. In one embodiment of the present invention, the residence timeof the acrylic acid mixture in the cooling step is less than about 30 s.In one embodiment of the present invention, the residence time of theacrylic acid mixture in the cooling step is between about 0.1 s andabout 10 s.

The liquid acrylic acid composition comprising acrylic acid, acrylicacid derivatives, or mixtures thereof produced according with thepresent invention can be purified using some or all of the processes ofextraction, drying, distilling, cooling, partial melting, and decantingdescribed in US20130274518A1 (incorporated herein by reference) toproduce crude and glacial acrylic acid. After purification, the crudeand glacial acrylic acid can be polymerized to produce a superabsorbentpolymer using processes that are similar to those described inUS20130274697A1 (incorporated herein by reference).

In one embodiment of the present invention, said crude acrylic acid isesterified with an alcohol to produce an acrylate monomer. Non-limitingexamples of alcohols are methanol, ethanol, butanol (n-butyl alcohol),2-ethyl hexanol, isobutanol, tert-butyl alcohol, hexyl alcohol, octylalcohol, isooctyl alcohol, lauryl alcohol, propyl alcohol, isopropylalcohol, hydroxyethyl alcohol, hydroxypropyl alcohol, and polyols, suchas hydroxyalkyl and alkylalkanolamine. In another embodiment of thepresent invention, said crude acrylic acid is esterified with methanol,ethanol, n-butyl alcohol, or 2-ethyl hexanol to produce methyl acrylatemonomer, ethyl acrylate monomer, n-butyl acrylate monomer, or2-ethylhexyl acrylate monomer, respectively. In yet another embodimentof the present invention, said methyl acrylate monomer, ethyl acrylatemonomer, n-butyl acrylate monomer, or 2-ethylhexyl acrylate monomer ispolymerized to produce methyl acrylate polymer, ethyl acrylate polymer,n-butyl acrylate polymer, or 2-ethylhexyl acrylate polymer,respectively. In even yet another embodiment of the present invention,said methyl acrylate monomer, ethyl acrylate monomer, n-butyl acrylatemonomer, or 2-ethylhexyl acrylate monomer is co-polymerized with othermonomer to produce methyl acrylate co-polymer, ethyl acrylateco-polymer, n-butyl acrylate co-polymer, or 2-ethylhexyl acrylateco-polymer, respectively. Non-limiting examples of other monomers arevinyl acetate and ethylene. In one embodiment of the present invention,said methyl acrylate polymer, ethyl acrylate polymer, n-butyl acrylatepolymer, or 2-ethylhexyl acrylate polymer is blended with methylmethacrylate (MMA) to produce blends of MMA and methyl acrylate polymer,blends of MMA and ethyl acrylate polymer, blends of MMA and n-butylacrylate polymer, or blends of MMA and 2-ethylhexyl acrylate polymer,respectively. Non-limiting applications of polymers, co-polymers, orblends are in surface coatings, paints, resins, adhesives, plastics, anddispersions. In another embodiment of the present invention, saidalcohol is bio-based alcohol. In yet another embodiment of the presentinvention, said other monomer is bio-based monomer. In even yet anotherembodiment of the present invention, said MMA is bio-based MMA.

In one embodiment of the present invention, the method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises contactingsaid hydroxypropionic acid, hydroxypropionic acid derivatives, andmixture thereof and said water vapor with said dehydration catalyst orsaid dehydration catalyst precursor mixture under conditions sufficientto produce acrylic acid, acrylic acid derivatives, or mixtures thereofin a yield of at least 50%. In another embodiment of the presentinvention, the method comprises contacting said hydroxypropionic acid,hydroxypropionic acid derivatives, and mixture thereof and said watervapor with said dehydration catalyst or said dehydration catalystprecursor mixture under conditions are sufficient to produce acrylicacid, acrylic acid derivatives, or mixtures thereof in a yield of atleast about 70%. In another embodiment of the present invention, themethod comprises contacting said hydroxypropionic acid, hydroxypropionicacid derivatives, and mixture thereof and said water vapor with saiddehydration catalyst or said dehydration catalyst precursor mixtureunder conditions are sufficient to produce acrylic acid, acrylic acidderivatives, or mixtures thereof in a yield of at least about 80%. Inanother embodiment of the present invention, the method conditions aresufficient to produce acrylic acid, acrylic acid derivatives, ormixtures thereof with a selectivity of at least about 50%. In anotherembodiment of the present invention, the method conditions aresufficient to produce acrylic acid, acrylic acid derivatives, ormixtures thereof with a selectivity of at least about 70%. In anotherembodiment of the present invention, the method conditions aresufficient to produce acrylic acid, acrylic acid derivatives, ormixtures thereof with a selectivity of at least about 80%. In anotherembodiment of the present invention, the method conditions aresufficient to produce acrylic acid, acrylic acid derivatives, ormixtures thereof with propionic acid as an impurity, wherein thepropionic acid selectivity is less than about 5%. In another embodimentof the present invention, the method conditions are sufficient toproduce acrylic acid, acrylic acid derivatives, or mixtures thereof withpropionic acid as an impurity, wherein the propionic acid selectivity isless than about 1%. In another embodiment of the present invention, themethod conditions are sufficient to produce acrylic acid, acrylic acidderivatives, or mixtures thereof with a conversion of saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof of more than about 50%. In another embodiment of the presentinvention, the method conditions are sufficient to produce acrylic acid,acrylic acid derivatives, or mixtures thereof with a conversion of saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof of more than about 80%.

Among the benefits attainable by the foregoing embodiments is the lowyield of side products. In one embodiment of the present invention, theconditions are sufficient to produce propionic acid in a yield of lessthan about 5% from hydroxypropionic acid. In another embodiment of thepresent invention, the conditions are sufficient to produce propionicacid in a yield of less than about 1%, from hydroxypropionic acid. Inone embodiment of the present invention, the conditions are sufficientto produce each of acetic acid, pyruvic acid, 1,2-propanediol,hydroxyacetone, acrylic acid dimer, and 2,3-pentanedione in a yield ofless than about 2% from hydroxypropionic acid present in the gaseousmixture. In another embodiment of the present invention, the conditionsare sufficient to produce each of acetic acid, pyruvic acid,1,2-propanediol, hydroxyacetone, acrylic acid dimer, and2,3-pentanedione in a yield of less than about 0.5%, fromhydroxypropionic acid present in the gaseous mixture. In one embodimentof the present invention, the conditions are sufficient to produceacetaldehyde in a yield of less than about 8% from hydroxypropionic acidpresent in the gaseous mixture. In another embodiment of the presentinvention, the conditions are sufficient to produce acetaldehyde in ayield of less than about 4% from hydroxypropionic acid present in thegaseous mixture. In another embodiment of the present invention, theconditions are sufficient to produce acetaldehyde in a yield of lessthan about 3%, from hydroxypropionic acid present in the gaseousmixture. These yields are believed to be, heretofore, unattainably low.Yet, these benefits are indeed achievable as further evidenced in theExamples set out below.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises: a)diluting an about 88 wt % lactic acid aqueous solution with water toform an about 20 wt % lactic acid aqueous solution; b) heating the about20 wt % lactic acid aqueous solution at a temperature from about 95° C.to about 100° C. to hydrolyze oligomers of the lactic acid, producing amonomeric lactic acid solution comprising at least about 95 wt % of thelactic acid in monomeric form based on the total amount of lactic acid,lactic acid derivatives, or mixtures thereof; c) combining the monomericlactic acid solution with nitrogen to form a liquid/gas blend; d)evaporating the liquid/gas blend in a evaporator with inside surface ofborosilicate glass with a residence time of about 0.5 s to about 0.6 sat a temperature between about 300° C. and about 375° C. to produce agas mixture comprising about 2.5 mol % lactic acid and about 50 mol %water; e) contacting said gas mixture with any dehydration catalystdisclosed in Section II (“Catalysts for the Conversion ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any dehydration catalyst precursor mixture disclosed inSection III (“Catalyst Preparation Method”) in a catalytic reactor withan interior surface of borosilicate glass at a GHSV of about 4,500 h⁻¹,at a temperature from about 325° C. to about 400° C. under a totalpressure from about 10 barg to about 25 barg producing the acrylic acid;and f) cooling the acrylic acid with a residence time between about 0.1s and about 10 s.

In one embodiment of the present invention, a method of making acrylicacid is provided. The method comprises contacting: (a) a gas mixturecomprising: i) lactic acid, ii) water, and iii) nitrogen, wherein saidlactic acid is present in an amount of about 2.5 mol % and wherein saidwater is present in an amount of about 50 mol % based on the total molesof said gas mixture, with (b) a dehydration catalyst precursor mixtureconsisting essentially of: (KPO₃)_(n) and SiO₂ in a weight ratio betweenabout 1:1 and about 1:7; wherein said contacting step of said gasmixture with said dehydration catalyst precursor mixture is performed ata temperature from about 325° C. to about 400° C., at a WHSV betweenabout 0.25 (g of lactic acid/g of catalyst·h) and about 1.0 (g of lacticacid/g of catalyst·h), and at a total pressure between about 10 barg andabout 25 barg, in a reactor having an interior surface material selectedfrom the group consisting of amorphous silica and borosilicate glass;whereby acrylic acid is produced as a result of said water and saidlactic acid being contacted with said dehydration catalyst precursormixture.

In one embodiment of the present invention, a method of making acrylicacid is provided. The method comprises contacting: (a) a gas mixturecomprising: i) lactic acid, ii) water, and iii) nitrogen, wherein saidlactic acid is present in an amount of about 2.5 mol % and wherein saidwater is present in an amount of about 50 mol % based on the total molesof said gas mixture, with (b) a dehydration catalyst precursor mixtureconsisting essentially of: (KPO₃)_(n) and BaSO₄ in a weight ratiobetween about 1:1.3 and about 1:3.2; wherein said contacting step ofsaid gas mixture with said dehydration catalyst precursor mixture isperformed at a temperature from about 325° C. to about 400° C., at aWHSV between about 0.2 (g of lactic acid/g of catalyst·h) and about 0.4(g of lactic acid/g of catalyst·h), and at a total pressure betweenabout 10 barg and about 25 barg, in a reactor having an interior surfacematerial selected from the group consisting of amorphous silica andborosilicate glass; whereby acrylic acid is produced as a result of saidwater and said lactic acid being contacted with said dehydrationcatalyst precursor mixture.

In one embodiment of the present invention, a method of making acrylicacid is provided. The method comprises contacting: (a) a gas mixturecomprising: i) lactic acid, ii) water, and iii) nitrogen, wherein saidlactic acid is present in an amount of about 2.5 mol % and wherein saidwater is present in an amount of about 50 mol % based on the total molesof said gas mixture, with (b) a dehydration catalyst precursor mixtureconsisting essentially of: (KPO₃)_(n) and BaTa₂O₆ in a weight ratio ofabout 1:3.9; wherein said contacting step of said gas mixture with saiddehydration catalyst precursor mixture is performed at a temperaturefrom about 325° C. to about 400° C., at a WHSV of about 0.16 (g oflactic acid/g of catalyst·h), and at a total pressure between about 10barg and about 25 barg, in a reactor having an interior surface materialselected from the group consisting of amorphous silica and borosilicateglass; whereby acrylic acid is produced as a result of said water andsaid lactic acid being contacted with said dehydration catalystprecursor mixture.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprisescontacting: a) alkyl lactates or a solution comprising alkyl lactatesand a solvent; b) water vapor; and c) any dehydration catalyst disclosedin Section II (“Catalysts for the Conversion of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) of the present invention; wherein the water partialpressure during said contacting step is equal to or greater than thewater partial pressure at the triple point of at least one of said oneor more amorphous phosphate salts or said one or more precursorphosphate salts in said dehydration catalyst or said dehydrationcatalyst precursor mixture; wherein said contacting step is performed ata temperature equal to or greater than the temperature at the triplepoint of at least one of said one or more amorphous phosphate salts orsaid one or more precursor phosphate salts in said dehydration catalystor said dehydration catalyst precursor mixture; and whereby said acrylicacid, acrylic acid derivatives, or mixtures thereof is produced as aresult of said water vapor and said alkyl lactate being contacted withsaid dehydration catalyst or said dehydration catalyst precursormixture. In another embodiment of the present invention, said alkyllactates are selected from the group consisting of methyl lactate, ethyllactate, butyl lactate, 2-ethylhexyl lactate, and mixtures thereof. Inanother embodiment of the present invention, said solvent is selectedfrom the group consisting of water, methanol, ethanol, butanol,2-ethylhexanol, isobutanol, isooctyl alcohol, and mixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing alkyl lactates or a solution comprising alkyl lactates anda solvent; b) optionally combining the alkyl lactates or the solutioncomprising the alkyl lactates and a solvent with an essentiallychemically inert gas to form a liquid/gas blend; c) evaporating saidalkyl lactates, or said solution comprising alkyl lactates and asolvent, or said liquid/gas blend to produce a gas mixture; and d)contacting said gas mixture with any dehydration catalyst disclosed inSection II (“Catalysts for the Conversion of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) under a water partial pressure of about 0.4 bar ormore to produce said acrylic acid, acrylic acid derivatives, or mixturesthereof.

A method for dehydrating glycerin to acrolein is provided. The methodcomprises contacting: (a) glycerin, (b) water vapor, and (c) anydehydration catalyst disclosed in Section II (“Catalysts for theConversion of Hydroxypropionic Acid or its Derivatives to Acrylic Acidor its Derivatives”) or any dehydration catalyst precursor mixturedisclosed in Section III (“Catalyst Preparation Method”) of the presentinvention; wherein the water partial pressure during said contactingstep is equal to or greater than the water partial pressure at thetriple point of at least one of said one or more amorphous phosphatesalts or said one or more precursor phosphate salts in said dehydrationcatalyst or said dehydration catalyst precursor mixture; wherein saidcontacting step is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate saltsin said dehydration catalyst or said dehydration catalyst precursormixture; and whereby said acrolein is produced as a result of said watervapor and said glycerin being contacted with said dehydration catalystor said dehydration catalyst precursor mixture.

A method for isomerization of lactic acid, lactic acid derivatives, ormixtures thereof into 3-hydroxypropionic acid, 3-hydroxypropionic acidderivatives, or mixtures thereof is provided. The method comprisescontacting: (a) 3-hydroxypropionic acid, 3-hydroxypropionic acidderivatives, or mixtures thereof, (b) water vapor, and (c) anydehydration catalyst disclosed in Section II (“Catalysts for theConversion of Hydroxypropionic Acid or its Derivatives to Acrylic Acidor its Derivatives”) or any dehydration catalyst precursor mixturedisclosed in Section III (“Catalyst Preparation Method”) of the presentinvention; wherein the water partial pressure during said contactingstep is equal to or greater than the water partial pressure at thetriple point of at least one of said one or more amorphous phosphatesalts or said one or more precursor phosphate salts in said dehydrationcatalyst or said dehydration catalyst precursor mixture; wherein saidcontacting step is performed at a temperature equal to or greater thanthe temperature at the triple point of at least one of said one or moreamorphous phosphate salts or said one or more precursor phosphate saltsin said dehydration catalyst or said dehydration catalyst precursormixture; and whereby said 3-hydroxypropionic acid, 3-hydroxypropionicacid derivatives, or mixtures thereof are produced as a result of saidwater vapor and said lactic acid, lactic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst or saiddehydration catalyst precursor mixture.

A method for reduction of hydroxypropionic acid, hydroxypropionic acidderivatives, and mixtures thereof into propionic acid, propionic acidderivatives, 1-propanol, 1-propanol derivatives, or mixtures thereof isprovided. The method comprises contacting: (a) hydroxypropionic acid,hydroxypropionic acid derivatives, and mixtures thereof; (b) watervapor, (c) hydrogen gas, and (d) any dehydration catalyst disclosed inSection II (“Catalysts for the Conversion of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) of the present invention; wherein the water partialpressure during said contacting step is equal to or greater than thewater partial pressure at the triple point of at least one of said oneor more amorphous phosphate salts or said one or more precursorphosphate salts in said dehydration catalyst or said dehydrationcatalyst precursor mixture; wherein said contacting step is performed ata temperature equal to or greater than the temperature at the triplepoint of at least one of said one or more amorphous phosphate salts orsaid one or more precursor phosphate salts in said dehydration catalystor said dehydration catalyst precursor mixture; and whereby saidpropionic acid, propionic acid derivatives, 1-propanol, 1-propanolderivatives, or mixtures thereof are produced as a result of said watervapor, said hydrogen gas, and said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof being contactedwith said dehydration catalyst or said dehydration catalyst precursormixture. In another embodiment of the present invention, saiddehydration catalyst or said dehydration catalyst precursor mixturefurther comprises one or more transition metals selected from the groups8 to 12 of the periodic table. Derivatives of propionic acid can bemetal or ammonium salts of propionic acid, alkyl esters of propionicacid, or a mixture thereof. Non limiting examples of metal salts ofpropionic acid are sodium propionate, potassium propionate, and calciumpropionate. Non limiting examples of alkyl esters of propionic acid aremethyl propionate, ethyl propionate, butyl propionate, 2-ethylhexylpropionate, or mixtures thereof. A derivative of 1-propanol can be1-alkyloxypropanol.

A method for dehydrating alcohols to alkenes is provided. The methodcomprises contacting: (a) one or more aliphatic alcohols, (b) watervapor, and (c) any dehydration catalyst disclosed in Section II(“Catalysts for the Conversion of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives”) or any dehydrationcatalyst precursor mixture disclosed in Section III (“CatalystPreparation Method”) of the present invention; wherein the water partialpressure during said contacting step is equal to or greater than thewater partial pressure at the triple point of at least one of said oneor more amorphous phosphate salts or said one or more precursorphosphate salts in said dehydration catalyst or said dehydrationcatalyst precursor mixture; wherein said contacting step is performed ata temperature equal to or greater than the temperature at the triplepoint of at least one of said one or more amorphous phosphate salts orsaid one or more precursor phosphate salts in said dehydration catalystor said dehydration catalyst precursor mixture; and whereby one or morealkenes are produced as a result of said water vapor and said one ormore aliphatic alcohols being contacted with said dehydration catalystor said dehydration catalyst precursor mixture. Non limiting examples ofalcohols are ethanol, n-propanol, isopropanol, n-butanol, sec-butanol,isobutanol, tert-butanol, pentanol, ethylene glycol, propylene glycol,glycerol, other polyhydric alcohols, and alicyclic alcohols.

V. Examples

The following examples are provided to illustrate the invention, but arenot intended to limit the scope thereof. Examples 1, 2, 5, 7, and 8describe the preparation of different catalysts in accordance withvarious embodiments of the present invention. Examples 3, 4, and 6describe the preparation of catalysts not according to the presentinvention. Example 9 describes the testing procedure of catalysts ofExamples 1 through 6, Example 10 describes the testing procedure of thecatalyst of Example 7, and Example 11 describes the testing procedure ofthe catalyst of Example 8. Examples 12 through 20 describe (XPO₃)_(n)catalysts and their testing results, where X is Cs, K, Na, Li, and Ba.Examples 21 through 26 describe K_(x)P_(y)O_(z) catalysts and theirtesting results, where x, y, and z are 5, 3, and 10; 2, 4, and 11; and4, 2, and 7. Finally, Examples 27, 28, and 29 compare the performance ofa (KPO₃)_(n) and fused silica catalyst with that of a (KPO₃)_(n) andalumina catalyst.

Example 1—(KPO₃)_(n) and BaSO₄ Catalyst

Barium sulfate (BaSO₄, 100 wt %, 30.0 g, 128.5 mmol; Aldrich, St. Louis,Mo.; catalog #202762) and potassium phosphate monobasic (KH₂PO₄, 99.995wt %, 23.33 g, 171.4 mmol; Fluka, St. Louis, Mo.; catalog #60216) werecombined and ground together for 15 min at 500 rpm using a planetaryball mill PM 100 (Retsch, Haan, Germany; catalog #20.540.0003), a 125 mLgrinding jar (Retsch, Haan, Germany; catalog #01.462.0136), and 7grinding balls (Retsch, Haan, Germany, catalog #05.368.0028) to obtain afine solid. The solid was transferred to a 600 mL glass beaker andcalcined at 450° C. for 12 h with a heating ramp of 2° C./min and usinga Nabertherm furnace N30/85 HA with P300 controller (Nabertherm,Lilienthal, Germany, catalog # N30/85 HA). After calcination, thematerial was kept inside the oven until it reached a temperature below80° C.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 90 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany, catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (28.5 g).The material was analyzed by XRD and BaSO₄ and T-(KPO₃)_(n) wereidentified as the components of the dehydration catalyst precursormixture.

Example 2—(KPO₃)_(n) and BaSO₄ Catalyst

Barium sulfate (BaSO₄, 100 wt %, 50.0 g, 214.2 mmol; Aldrich, St. Louis,Mo.; catalog #202762) and potassium phosphate monobasic (KH₂PO₄, 100 wt%, 19.44 g, 142.8 mmol; Fluka, St. Louis, Mo.; catalog #60216) werecombined and ground together for 15 min at 500 rpm using a planetaryball mill PM 100 (Retsch, Haan, Germany; catalog #20.540.0003), a 125 mLgrinding jar (Retsch, Haan, Germany; catalog #01.462.0136), and 7grinding balls (Retsch, Haan, Germany, catalog #05.368.0028) to obtain afine solid. The solid was transferred to a 600 mL glass beaker andcalcined at 450° C. for 12 h with a heating ramp of 2° C./min and usinga Nabertherm furnace N30/85 HA with P300 controller (Nabertherm,Lilienthal, Germany, catalog # N30/85 HA). After calcination, thematerial was kept inside the oven until it reached a temperature below80° C.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany, catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solids retained on sieve No. 140 were re-sieved for 30 minto obtain a catalyst with particle size between 106 μm and 212 μm (24.2g). The material was analyzed by XRD and BaSO₄ and T-(KPO₃)_(n) wereidentified as the components of the dehydration catalyst precursormixture.

Example 3 (Comparative)—BaSO₄ Catalyst

Barium sulfate (BaSO₄, 100 wt %, 30.0 g, 128.5 mmol; Aldrich, St. Louis,Mo.; catalog #202762) was weighed, transferred to a 600 mL glass beaker,and calcined at 450° C. for 12 h with a heating ramp of 2° C./min andusing a Nabertherm furnace N30/85 HA with P300 controller (Nabertherm,Lilienthal, Germany, catalog # N30/85 HA). After calcination, thematerial was kept inside the oven until it reached a temperature below80° C.

The calcined solid was sieved using a vibratory sieve shaker AS 200control (Retsch, Haan, Germany; catalog #30.018.0001), and sieves No. 70and 400 (USA standard testing sieve, ASTM E-11 specifications; GilsonCompany, Lewis Center, Ohio) until constant weight. The material withparticle size over 38 μm (3.4 g) was used as catalyst. After XRDanalysis, BaSO₄ was identified as the only component.

Example 4 (Comparative)—(KPO₃)_(n) and K₂SO₄ Catalyst

Potassium sulfate (K₂SO₄, 99.99 wt %, 30.0 g, 172.1 mmol; Aldrich, St.Louis, Mo., catalog #204129) and potassium phosphate monobasic (KH₂PO₄,99.995 wt %, 31.24 g, 229.5 mmol; Fluka, St. Louis, Mo., catalog #60216)were combined and ground together for 15 min at 500 rpm using aplanetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 7 grinding balls (Retsch, Haan, Germany, catalog#05.368.0028) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached atemperature below 80° C.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 90 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany, catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved untilconstant weight to obtain a catalyst with particle size between 106 μmand 212 μm (11.8 g). The material was analyzed by XRD and K₂SO₄ andT-(KPO₃)_(n) were identified as the components of the dehydrationcatalyst precursor mixture.

Example 5—(KPO₃)_(n) and BaTa₂O₆ and Ba₃Ta₅O₁₅ and Ba₃Ta₂O₈ Catalyst

Barium tantalate (BaTa₂O₆, 97.1 wt %, 40.0 g, 65.3 mmol; Alfa, WardHill, Mass., catalog #39179) and potassium phosphate monobasic (KH₂PO₄,99.995 wt %, 11.84 g, 87.0 mmol; Fluka, St. Louis, Mo., catalog #60216)were combined and ground together for 15 min at 500 rpm using aplanetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 7 grinding balls (Retsch, Haan, Germany, catalog#05.368.0028) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached atemperature below 80° C.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany, catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (21.2 g).The material was analyzed by XRD and BaTa₂O₆, Ba₃Ta₅O₁₅, Ba₃Ta₂O₈, andT-(KPO₃) were identified as the components of the dehydration catalystprecursor mixture.

Example 6 (Comparative)—BaTa₂O₆ and Ba₃Ta₅O₁₅ and Ba₃Ta₂O₈ Catalyst

Barium tantalate (BaTa₂O₆, 97.1 wt %, 40.0 g, 65.3 mmol; Alfa, WardHill, Mass., catalog #39179) was weighed, transferred to a 600 mL glassbeaker, and calcined at 450° C. for 12 h with a heating ramp of 2°C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached atemperature below 80° C.

The calcined solid was sieved using a vibratory sieve shaker AS 200control (Retsch, Haan, Germany; catalog #30.018.0001), and sieves No. 70and 400 (USA standard testing sieve, ASTM E-11 specifications; GilsonCompany, Lewis Center, Ohio) until constant weight. The material withparticle size over 38 μm (41.5 g) was used as catalyst. After XRDanalysis, BaTa₂O₆, Ba₃Ta₅O₁₅, and Ba₃Ta₂O₈ were identified as thecomponents of the dehydration catalyst precursor mixture.

Example 7—(KPO₃)_(n) and Quartz Silica Catalyst

Potassium phosphate monobasic (KH₂PO₄, 99.995 wt %, 20.00 g, 147.0 mmol;Fluka, St. Louis, Mo., catalog #60216) and silicon oxide quartz(crystalline SiO₂, 49.44 g; Alfa, Ward Hill, Mass., catalog #13024) werecombined and ground together using a mortar and pestle to obtain a finesolid. Then, the material was transferred to a 600 mL glass beaker andcalcined at 450° C. for 12 h with a heating ramp of 2° C./min and usinga Nabertherm furnace N30/85 HA with P300 controller (Nabertherm,Lilienthal, Germany, catalog # N30/85 HA). After calcination, thematerial was kept inside the oven until it reached a temperature below80° C.

The calcined solid was ground gently using a mortar and pestle. Then,the solids were sieved for 5 min using a vibratory sieve shaker AS 200control (Retsch, Haan, Germany; catalog #30.018.0001), and sieves No. 70and 140 (USA standard testing sieve, ASTM E-11 specifications; GilsonCompany, Lewis Center, Ohio). The process of grinding particles retainedon sieve No. 70 followed by sieving was repeated until all the materialpassed sieve No. 70. Finally, the solid retained on sieve No. 140 wasre-sieved for 30 min to obtain a catalyst with particle size between 106μm and 212 μm (20.7 g). The material was analyzed by XRD andT-(KPO₃)_(n) and SiO₂ were identified as the components of thedehydration catalyst precursor mixture.

Example 8—26 wt % (KPO₃)_(n) and 74 wt % Fused Silica Catalyst

Dipotassium phosphate (K₂HPO₄, 100 wt %, 40.00 g, 229.6 mmol; Fluka, St.Louis, Mo., catalog #60347), ammonium phosphate dibasic ((NH₄)₂HPO₄,97.7 wt %, 31.04 g, 229.6 mmol; Aldrich, St. Louis, Mo., catalog#379980), and amorphous silicon oxide (fused silica; SiO₂, 154.34 g;Aldrich, St. Louis, Mo., catalog #342831) were combined and groundtogether for 15 min at 500 rpm using a planetary ball mill PM 100(Retsch, Haan, Germany; catalog #20.540.0003), a 500 mL grinding jar(Retsch, Haan, Germany; catalog #01.462.0227), and 25 grinding balls(Retsch, Haan, Germany, catalog #05.368.0093) to obtain a fine solid.The solid was transferred to a 1000 mL glass beaker and calcined at 450°C. for 12 h with a heating ramp of 2° C./min and using a Naberthermfurnace N30/85 HA with P300 controller (Nabertherm, Lilienthal, Germany,catalog # N30/85 HA). After calcination, the material was kept insidethe oven until it reached room temperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0227), and 5 grinding balls (Retsch, Haan, Germany, catalog#05.368.0093). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (40.14g). The material was analyzed by XRD and T-(KPO₃)_(n) was identified asa component of the dehydration catalyst precursor mixture.

Example 9

Dehydration catalyst precursor mixtures prepared as described inExamples 1 to 6 were tested for the conversion of lactic acid to acrylicacid as follows. The reactions were carried out in a flow reactor systemwith temperature and mass flow controllers. The reactors were made ofquartz (28 mm L×2 mm I.D.), housed in a heating block, and fed at thetop with separate liquid and gas feeds through silica capillaries. Thesefeeds were mixed together and heated gradually to 375° C. at 25 bargbefore reaching the dehydration catalyst bed. Volumes of dehydrationcatalyst precursor mixture of about 200 μL, placed on an isothermalheating zone at 375° C. (±1° C.), were used. The gas feed was composedof nitrogen (N₂, 6 NmL/min) and helium (He, 0.15 NmL/min), which wasadded as an internal standard for gas chromatograph (GC) analysis. Theliquid feed was an aqueous solution of lactic acid (20 wt % L-lacticacid, 5 μL/min) prepared by mixing a commercial solution of lactic acid(ACS reagent, >85 wt %; Sigma-Aldrich, St. Louis, Mo., catalog #252476)with deionized water, followed by heating at 95° C. for 12 h and coolingto room temperature. The water partial pressure is calculated as 168.1psi.

The reactor effluent was connected to another nitrogen line, whichdiluted the effluent by a factor of two. The helium internal standardnormalized any variation in this dilution for analytical purposes. Thedehydration catalysts were equilibrated for 6 h by contacting them withthe mixed liquid and gas feeds, after which the condensed products werecollected every 6 h by a liquid sampling system cooled to 10° C.Typically, 48 hour experiments were performed and 5 liquid samples werecollected. These liquid samples were analyzed by offline highperformance liquid chromatography (HPLC) and offline gas chromatography(GC). The gaseous products accumulated on the overhead space of thecollection vials and were analyzed using sampling valves and online gaschromatography (GC).

The offline HPLC analyses were performed using an Agilent 1200 Seriesinstrument equipped with a diode-array detector (Agilent Technologies,Santa Clara, Calif.) and an Atlantis T3 column (250 mm L×4.6 mm I.D.×5micron; Waters, Milford, Mass.) using methods generally known by thosehaving ordinary skill in the art to determine concentrations of acrylicacid and lactic acid.

The offline GC analyses were performed using a dual Channel TraceGC(Interscience, Breda, Netherlands) equipped with a FID detector and aDB-624 column (30 μm L×0.25 mm I.D.×1.4 μm; Agilent Technologies, SantaClara, Calif.) using methods generally known by those having ordinaryskill in the art to determine concentrations of acetaldehyde, aceticacid, acetone, acrylic acid, acrylic acid dimer, ethanol,hydroxyacetone, 2,3-pentanedione, 3-pentanone, propanal, propionic acid,and propanol.

The online GC analyses were performed using a CompactGC (Interscience,Breda, Netherlands) with three channels equipped with a FID detectorcoupled to a Rtx-624 column (30 m L×0.25 mm I.D×1.4 μm; Restek,Bellefonte, Pa.), a TDC detector coupled to a Rt Q-bond column (30 mL×0.32 mm; Restek, Bellefonte, Pa.), and a TDC detector coupled to a Molsieve MS5A column (10 m, Restek Corp., Bellefonte, Pa.) using methodsgenerally known by those having ordinary skill in the art to determineconcentrations of He, CO, CO₂, acetaldehyde, methane, ethylene, ethane,propane, and propylene.

Example 10

The dehydration catalyst precursor mixture prepared as described inExample 7 was tested for the conversion of lactic acid to acrylic acidas follows. A glass-lined stainless steel tube (14″ or 356 mm length, 4mm internal diameter; SGE Analytical Science Pty Ltd., Ringwood,Australia) was packed with glass wool at the bottom (0.64 cm³, 2″ or 51mm, outside the heating zone), followed by dehydration catalystprecursor mixture in the middle (1.9 cm³ bed volume, 6″ or 152 mm bedlength, inside the heating zone) and free space at the top (0.64 cm³, 2″or 51 mm, inside the heating zone; 1.3 cm³, 4″ or 102 mm, outside theheating zone). The tube was placed inside an aluminum block and a clamshell furnace series 3210 (Applied Test Systems, Butler, Pa.) in adown-flow arrangement and the bottom of the reactor was connected to aPTFE-coated catch tank using a fused silica lined stainless steel tubing(⅛″ or 3.2 mm external diameter; Supelco, St. Louis, Mo.) and Swagelok™fittings. The reactor was purged by flowing N₂ gas (45 mL/min) at 360psig (25 barg) using a Brooks gas flow controller (Hatfield, Pa.) and aBrooks back pressure regulator. Then, the reactor was heated (1° C./minramp) until a final temperature of about 375° C. (tube wall temperature)was reached. A liquid solution of lactic acid in water (20.0 wt %) wasfed at the top of the reactor at 0.045 mL/min thoughpolyetheretherketone (PEEK™) tubing ( 1/16″ or 1.6 mm external diameter;Upchurch Scientific, Oak Harbor, Wash.) using an Azura P4.1S Knauer pump(Berlin, Germany). Before contacting the dehydration catalyst, the gasphase concentrations were: nitrogen: 47.9 mol %; lactic acid: 2.5 mol %;and water: 49.6 mol % and the water partial pressure was 185.8 psi (12.8bar). After contacting the dehydration catalyst, the reactor effluentwas cooled and the liquid was collected in the catch tank and sampledperiodically for analysis by offline HPLC using an Agilent 1100 system(Santa Clara, Calif.) equipped with a diode array detector and a WatersAtlantis T3 column (250 mm L×4.6 mm I.D.×5 micron; Waters, Milford,Mass.) and by offline GC using a Hewlett Packard HP6890 series system(Santa Clara, Calif.) equipped with a FID detector and Agilent CP-Wax 58FFAP CB column (Clara, Calif.), using methods generally known by thosehaving ordinary skill in the art. The uncondensed gas effluents weredischarged and analyzed periodically by online GC using an Agilent 7890system (Santa Clara, Calif.) equipped with a FID detector and VarianCP-Para Bond Q column (Catalog # CP7351; Santa Clara, Calif.).

Time on stream (TOS) was 23 h, acrylic acid yield was 80.4 mol %, lacticacid conversion was 100 mol %, acrylic acid selectivity was 80.4 mol %,and propionic acid selectivity was 0.7 mol %.

Example 11

The dehydration catalyst precursor mixture prepared as described inExample 8 was tested for the conversion of lactic acid to acrylic acidas follows. A sample of dehydration catalyst precursor mixture wasmanually blended with amorphous silicon oxide (SiO₂, 1.37 g; pre-groundand sieved to 106-212 μm; Aldrich, St. Louis, Mo., catalog #342831). Aglass-lined stainless steel tube (14″ or 356 mm length, 4 mm internaldiameter; SGE Analytical Science Pty Ltd., Ringwood, Australia) waspacked with glass wool at the bottom (0.80 cm³, 2.5″ or 64 mm, outsidethe heating zone), followed by the blend of silicon oxide anddehydration catalyst precursor mixture in the middle (2.55 cm³ bedvolume, 8″ or 203 mm bed length, inside the heating zone) and free spaceat the top (1.10 cm³, 3.5″ or 89 mm, outside the heating zone). The tubewas placed inside an aluminum block and a clam shell furnace series 3210(8″ length heating zone; Applied Test Systems, Butler, Pa.) in adown-flow arrangement and the bottom of the reactor was connected to aPTFE-coated catch tank using a fused silica lined stainless steel tubing(⅛″ or 3.2 mm external diameter; Supelco, St. Louis, Mo.) and Swagelok™fittings. The reactor was pressurized to 360 psig (25 barg) using aBrooks gas flow controller (Hatfield, Pa.) and a Brooks back pressureregulator and purged by flowing N₂ gas (45 mL/min). Then, the reactorwas heated (1° C./min ramp) until a final temperature of about 375° C.(tube wall temperature) was reached. A liquid solution of lactic acid inwater (20.0 wt %) was fed at the top of the reactor at 0.045 mL/minthough polyetheretherketone (PEEK™) tubing ( 1/16″ or 1.6 mm externaldiameter; Aldrich, St. Louis, Mo., catalog # ZA227293) using a Smartline100 Knauer pump (Berlin, Germany). Before contacting the dehydrationcatalyst, the gas phase concentrations were: 47.9 mol % nitrogen, 2.5mol % lactic acid, and 49.6 mol % water; and the water partial pressurewas 185.8 psi (12.8 bar). After contacting the dehydration catalyst, thereactor effluent was cooled and the liquid was collected in the catchtank and sampled periodically for analysis by offline HPLC using anAgilent 1100 system (Santa Clara, Calif.) equipped with a diode arraydetector and a Waters Atlantis T3 column (250 mm L×4.6 mm I.D.×5 micron;Waters, Milford, Mass.) and by offline GC using a Hewlett Packard HP6890series system (Santa Clara, Calif.) equipped with a FID detector andAgilent CP-Wax 58 FFAP CB column (Clara, Calif.), using methodsgenerally known by those having ordinary skill in the art. Theuncondensed gas effluents were discharged and analyzed periodically byonline GC using an Agilent 7890 system (Santa Clara, Calif.) equippedwith a FID detector and Varian CP-Para Bond Q column (Catalog # CP7351;Santa Clara, Calif.).

Time on stream (TOS) was 50.4 h, acrylic acid yield was 85.1 mol %,lactic acid conversion was 98.3 mol %, acrylic acid selectivity was 86.6mol %, and propionic acid selectivity was 0.3 mol %.

Table 1 describes the results for the different lactic acid conversionreactions using catalysts prepared as described in Examples 1 through 8.Table 1 provides a convenient comparison of the conversion of lacticacid to acrylic acid using catalysts according to the invention (i.e.,Examples 1, 2, 5, 7, and 8) and those not according to the invention(i.e., Examples 3, 4, and 6).

TABLE 1 Results from testing of various catalysts Water Catalyst PartialCatalyst Precursor AAY, LAC, AAS, PAS, Pressure, Example CompositionTOS, [h] [mol %] [mol %] [mol %] [mol %] [psi] Examples according to thepresent invention 1 (KPO₃)_(n) + 67 74.7 90.8 82.2 0.7 168.1 BaSO₄ 2(KPO₃)_(n) + 117 71.0 91.9 77.2 0.8 168.1 BaSO₄ 5 (KPO₃)_(n) + 68 63.394.9 67.2 1.7 168.1 BaTa₂O₆ + Ba₃Ta₅O₁₅ + Ba₃Ta₂O₈ 7 (KPO₃)_(n) + 2380.4 100 80.4 0.7 185.8 quartz SiO₂ 8 (KPO₃)_(n) + 50.4 85.1 98.3 86.60.3 185.8 amorphous SiO₂ Examples not according to the present invention3 BaSO₄ 118 2.3 36.2 6.5 6.5 168.1 4 (KPO₃)_(n) + 117 1.4 30.5 4.5 5.7168.1 K₂SO₄ 6 BaTa₂O₆ + 117 2.6 40.9 6.4 9.9 168.1 Ba₃Ta₅O₁₅ + Ba₃Ta₂O₈

Example 12—26 wt % (CsPO₃)_(n) and 74 wt % Fused Silica Catalyst

Cesium nitrate (CsNO₃, 99.99 wt %, 30.00 g; Aldrich, St. Louis, Mo.,catalog #202150), ammonium phosphate dibasic ((NH₄)₂HPO₄, 97.7 wt %,20.80 g; Aldrich, St. Louis, Mo., catalog #379980), and amorphoussilicon oxide (SiO₂, 72.03 g; Aldrich, St. Louis, Mo., catalog #342831)were combined and ground together for 15 min at 500 rpm using aplanetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0227), and 25 grinding balls (Retsch, Haan, Germany, catalog#05.368.0093) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached roomtemperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany), and 6grinding balls (Retsch, Haan, Germany). Then, the solids were sieved for5 min using a vibratory sieve shaker AS 200 control (Retsch, Haan,Germany; catalog #30.018.0001), and sieves No. 70 and 140 (USA standardtesting sieve, ASTM E-11 specifications; Gilson Company, Lewis Center,Ohio). The process of grinding particles retained on sieve No. 70followed by sieving was repeated until all the material passed sieve No.70. Finally, the solid retained on sieve No. 140 was re-sieved for 30min to obtain a catalyst with particle size between 106 μm and 212 μm(34.1 g). The material was analyzed by XRD and (CsPO₃)_(n) and Cs₄P₂O₇were identified as components of the dehydration catalyst precursormixture.

Example 13

A stainless steel glass-lined tube reactor (SGE Analytical Science PtyLtd., Ringwood, Australia; P/N: 0827671) with 6.4 mm (¼ in.) OD, 4 mmID, and 35.6 cm (14 in.) length was packed in 3 zones as follows: 1)bottom zone: quartz wool was packed to give a bottom zone length of 7.6cm (3 in.); 2) middle zone/dehydration zone: 1.4 g of the catalystprepared in Example 12 were mixed with 1.4 g of fused silica(Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831; ground and sievedto 102-212 μm) to form a 13 wt % (CsPO₃)_(n) and 87 wt % fused silicacatalyst and then packed to give a catalyst bed length of 20.3 cm (8in.; 2.5 mL catalyst bed volume); and 3) top zone/evaporator zone wasempty and 7.6 cm (3 in.) in length.

The reactor was first placed inside an 8 in. long aluminum block suchthat the top of the catalyst bed and the top of the aluminum block arealigned. Then, the aluminum block and the reactor were placed in aSeries 3210 8 in. long clam shell furnace (Applied Test Systems, Butler,Pa.). The reactor was set-up in a down-flow arrangement and was equippedwith a Knauer Smartline 100 feed pump (Knauer GmbH, Berlin, Germany), aBrooks 0254 gas flow controller (Brooks Instrument LLC, Hatfield, Pa.),a Brooks back pressure regulator, and a Teflon-lined catch tank. Thehead of the reactor was fitted with a 1.6 mm ( 1/16 in.) stainless steelline, as a nitrogen feed line, and a 1.6 mm ( 1/16 in.)polyetheretherketone (PEEK™) tubing (Supelco Inc., Bellefonte, Pa.), asa liquid feed supply line connected to the feed pump. The bottom of thereactor was connected to the catch tank using a 3.2 mm (⅛ in.) fusedsilica lined stainless steel tubing and Swagelok™ fittings. The clamshell furnace was heated such that the reactor wall temperature was keptconstant at about 375° C. during the course of the reaction.

The reactor was fed with separate liquid and gas feeds, which were mixedtogether before reaching the catalyst bed. The inert gas was nitrogen at24.8 barg (360 psig) pressure and was fed into the reactor at a rate of45 mL/min (under STP conditions). The liquid feed was an aqueoussolution of lactic acid (20 wt % L-lactic acid) and was fed into thereactor at a rate of 0.045 mL/min. After the evaporation zone, theresulting gas feed stream had the following composition: 49.8 mol %water, 47.8 mol % nitrogen, and 2.5 mol % lactic acid. In thedehydration zone, the GHSV was about 2,215 h⁻¹, WHSV was about 0.4 h⁻¹,and water partial pressure was about 13 bar (186 psi).

The gas product stream was cooled and analyzed on-line by an Agilent7890A GC (Agilent Technologies, Inc., Santa Clara, Calif.) equipped witha FID detector and Varian CP-PoraBond Q column (Agilent Technologies,Inc., Santa Clara, Calif.; Catalog # CP7351). The liquid product streamwas collected in the catch tank and analyzed off-line (using methodsgenerally known by those having ordinary skill in the art) using anAgilent 1100 HPLC (Agilent Technologies, Inc., Santa Clara, Calif.),equipped with a diode array detector (DAD) and an Atlantis T3 column(Waters Corp., Milford, Mass.; Catalog #186003748), and a HewlettPackard HP6890 series GC (Agilent Technologies, Inc., Santa Clara,Calif.), equipped with an FID detector and Agilent CP-Wax 58 FFAP CBcolumn (Agilent Technologies, Inc., Santa Clara, Calif.; Catalog #CP7717).

The liquid product stream was cooled and collected over a period ofabout 3 h. The overall acrylic acid yield (AAY) was 83.3 mol %, acrylicacid selectivity (AAS) was 83.3 mol %, lactic acid conversion (LAC) was100 mol %, and propionic acid selectivity (PAS) was 0.21 mol %.

Then, with all other conditions remaining the same as above, we variedthe nitrogen and water partial pressures at various reactiontemperatures and the results are shown in Table 2 below. The time onstream (TOS) for each of these conditions was about 3 h.

TABLE 2 Results from testing of the catalyst: 13 wt % (CsPO₃)_(n) and 87wt % fused silica Water Reaction Nitrogen Partial T, Pressure, Pressure,AAY, LAC, AAS, PAS, [° C.] [psi] [psi] [mol %] [mol %] [mol %] [mol %]350 360 186.4 77.7 92.5 84 0.36 160 86.9 79.1 89.6 88.3 0.28 20 17.261.8 76.1 81.4 0.40 375 360 186.4 83.3 100 83.3 0.21 160 86.9 87.4 10087.4 0.29 80 47 88.4 100 88.4 0.42 40 27.1 85.1 95.9 88.8 0.53 20 17.283.8 95.1 88.2 0.61 400 360 186.4 79 100 79 0.82 160 86.9 89.3 100 89.30.79 20 17.2 78.7 94 83.8 1.58

Example 14

1.315 g of the catalyst prepared in Example 8 were mixed with 1.315 g offused silica (Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831;ground and sieved to 102-212 μm) to form a 13 wt % (KPO₃)_(n) and 87 wt% fused silica catalyst and tested in the experimental setup of andusing the same procedure as in Example 13. The results are shown inTable 3 below.

TABLE 3 Results from testing of the catalyst: 13 wt % (KPO₃)_(n) and 87wt % fused silica Water Reaction Nitrogen Partial T, Pressure, Pressure,AAY, LAC, AAS, PAS, [° C.] [psi] [psi] [mol %] [mol %] [mol %] [mol %]350 360 186.4 77.6 84.6 91.8 0.05 160 86.9 72.7 78.9 92.2 0 375 360186.4 84.7 100 84.7 N/A 160 86.9 85.8 100 85.8 N/A 80 47 45.9 56.5 81.20.33 400 360 186.4 89.4 97.1 92.1 0.18 160 86.9 89.8 100 89.8 0.15

Example 15—26 wt % (NaPO₃)_(n) and 74 wt % Fused Silica Catalyst

Disodium phosphate (Na₂HPO₄, 99.999 wt %, 20.00 g; Fluka, St. Louis,Mo., catalog #71629), ammonium phosphate dibasic ((NH₄)₂HPO₄, 97.7 wt %,19.04 g; Aldrich, St. Louis, Mo., catalog #379980), and amorphoussilicon oxide (SiO₂, 81.77 g; Aldrich, St. Louis, Mo., catalog #342831)were combined and ground together for 15 min at 500 rpm using aplanetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0227), and 25 grinding balls (Retsch, Haan, Germany, catalog#05.368.0093) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached roomtemperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany; catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (45.0 g).The material was analyzed by XRD and Na₃P₃O₉ and (NaPO₃)_(n) wereidentified as components of the dehydration catalyst precursor mixture.

Example 16

1.35 g of the catalyst prepared in Example 15 were mixed with 1.35 g offused silica (Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831;ground and sieved to 102-212 μm) to form a 13 wt % (NaPO₃)_(n) and 87 wt% fused silica catalyst and tested in the experimental setup of andusing the same procedure as in Example 13. The results are shown inTable 4 below.

TABLE 4 Results from testing of the catalyst: 13 wt % (NaPO₃)_(n) and 87wt % fused silica Water Reaction Nitrogen Partial T Pressure, Pressure,AAY, LAC, AAS, PAS, [° C.] [psi] [psi] [mol %] [mol %] [mol %] [mol %]350 360 186.4 35.6 54.6 65.3 0 160 86.9 23.3 40.3 57.8 0 80 47 9.3 29.831.4 0.21 375 360 186.4 56.7 88.6 64.1 0.02 160 86.9 42.6 68.4 62.3 0.08400 460 236.2 62 90.9 68.2 0.14 360 186.4 57.2 89.5 63.9 0.12 160 86.947.3 81.6 57.9 0.12 80 47 38.1 79.9 47.6 49.1

Note that an extrapolation of the AAS data at either 400° C. or 375° C.to higher nitrogen pressures yields AAS of 90 mol % at pressure of about1,200 psi, or equivalently, water partial pressure of about 605 psi. Atthose pressures, we expect that the LAC would be 100 mol % and the AAYwould be 90 mol %.

Example 17 (Comparative)—26 wt % (LiPO₃)_(n) and 74 wt % Fused SilicaCatalyst

Lithium nitrate (LiNO₃, 92.4 wt %, 20.00 g; Aldrich, St. Louis, Mo.,catalog #229741), ammonium phosphate dibasic ((NH₄)₂HPO₄, 97.7 wt %,36.23 g; Aldrich, St. Louis, Mo., catalog #379980), and amorphoussilicon oxide (SiO₂, 60.09 g; Aldrich, St. Louis, Mo., catalog #342831)were combined and ground together for 15 min at 500 rpm using aplanetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0227), and 25 grinding balls (Retsch, Haan, Germany, catalog#05.368.0093) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached roomtemperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany; catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (36.3 g).The material was analyzed by XRD and (LiPO₃)_(n) was identified as acomponent of the dehydration catalyst precursor mixture.

Example 18 (Comparative)

1.44 g of the catalyst prepared in Example 17 were mixed with 1.44 g offused silica (Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831;ground and sieved to 102-212 μm) to form a 13 wt % (LiPO₃)_(n) and 87 wt% fused silica catalyst and tested in the experimental setup of andusing the same procedure as in Example 13 (in this Example 18, the WHSVwas about 0.38 h⁻¹). The results are shown in Table 5 below.

TABLE 5 Results from testing of the catalyst: 13 wt % (LiPO₃)_(n) and 87wt % fused silica Water Reaction Nitrogen Partial T Pressure, Pressure,AAY, LAC, AAS, PAS, [° C.] [psi] [psi] [mol %] [mol %] [mol %] [mol %]350 360 186.4 1.3 68.6 1.9 0.13 160 86.9 0.8 69.5 1.2 0.18 375 450 231.34.7 100 4.7 0.28 360 186.4 11.8 100 11.8 0.03 160 86.9 1.6 93.7 1.7 0.35400 360 186.4 6.6 100 6.6 1.1

Example 19 (Comparative)—26 wt % (Ba(PO₃)₂)_(n) and 74 wt % Fused SilicaCatalyst

Barium nitrate (Ba(NO₃)₂, 95.91 wt %, 25.00 g; Aldrich, St. Louis, Mo.,catalog #202754), ammonium phosphate dibasic ((NH₄)₂HPO₄, 97.7 wt %,24.80 g; Aldrich, St. Louis, Mo., catalog #379980), and amorphoussilicon oxide (SiO₂, 77.10 g; Aldrich, St. Louis, Mo., catalog #342831)were combined and ground together for 15 min at 500 rpm using aplanetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0227), and 25 grinding balls (Retsch, Haan, Germany, catalog#05.368.0093) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached roomtemperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany; catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (22.7 g).The material was analyzed by XRD and (Ba(PO₃)₂)_(n) was identified as acomponent of the dehydration catalyst precursor mixture.

Example 20 (Comparative)

1.3 g of the catalyst prepared in Example 19 were mixed with 1.3 g offused silica (Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831;ground and sieved to 102-212 μm) to form a 13 wt % (Ba(PO₃)₂)_(n) and 87wt % fused silica catalyst and tested in the experimental setup of andusing the same procedure as in Example 13 (in this Example 20, thebottom zone was 6.4 cm (2.5 in.) in length). The liquid product streamwas cooled and collected over a period of about 5 h. The overall acrylicacid yield (AAY) was 2 mol %, acrylic acid selectivity (AAS) was 2 mol%, lactic acid conversion (LAC) was 100 mol %, propionic acidselectivity (PAS) was 0.37 mol %, and acetaldehyde yield was about 95mol %.

Table 6 below shows selective results from Tables 2 through 5, andExamples 19 and 20 to compare the effect of metal X in the catalyst(XPO₃)_(n) on the performance.

TABLE 6 Results from catalysts (XPO₃)_(n) and fused silica at 375° C.and various pressures. Nitro- Water gen Partial Pres- Pres- Metal X;sure, sure, AAY, LAC, AAS, PAS, Catalyst [psi] [psi] [mol %] [mol %][mol %] [mol %] Example not according to the present invention X = Li;360 186.4 11.8 100 11.8 0.03 (LiPO₃)_(n) 160 86.9 1.6 93.7 1.7 0.35Examples according to the present invention X = Na; 360 186.4 56.7 88.664.1 0.02 (NaPO₃)_(n) 160 86.9 42.6 68.4 62.3 0.08 X = K; 360 186.4 84.7100 84.7 N/A (KPO₃)_(n) 160 86.9 85.8 100 85.8 N/A X = Cs; 360 186.483.3 100 83.3 0.21 (CsPO₃)_(n) 160 86.9 87.4 100 87.4 0.29 Example notaccording to the present invention X = Ba; 360 186.4 2 100 2 0.37(Ba(PO₃)₂)_(n)

Example 21—26 wt % K₅P₃O₁₀ and 74 wt % Fused Silica Catalyst

Dipotassium phosphate (K₂HPO₄, 100 wt %, 30.00 g; Fluka, St. Louis, Mo.,catalog #60347), ammonium phosphate dibasic ((NH₄)₂HPO₄, 97.7 wt %, 4.66g; Aldrich, St. Louis, Mo., catalog #379980), and amorphous siliconoxide (SiO₂, 87.93 g; Aldrich, St. Louis, Mo., catalog #342831) werecombined and ground together for 15 min at 500 rpm using a planetaryball mill PM 100 (Retsch, Haan, Germany; catalog #20.540.0003), a 500 mLgrinding jar (Retsch, Haan, Germany; catalog #01.462.0227), and 25grinding balls (Retsch, Haan, Germany, catalog #05.368.0093) to obtain afine solid. The solid was transferred to a 600 mL glass beaker andcalcined at 450° C. for 12 h with a heating ramp of 2° C./min and usinga Nabertherm furnace N30/85 HA with P300 controller (Nabertherm,Lilienthal, Germany, catalog # N30/85 HA). After calcination, thematerial was kept inside the oven until it reached room temperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany; catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (12.9 g).The material was analyzed by XRD and K₅P₃O₁₀.2H₂O was identified as acomponent of the dehydration catalyst precursor mixture.

Example 22

1.155 g of the catalyst prepared in Example 21 were mixed with 1.155 gof fused silica (Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831;ground and sieved to 102-212 μm) to form a 13 wt % K₅P₃O₁₀ and 87 wt %fused silica catalyst and tested in the experimental setup of and usingthe same procedure as in Example 13 (in this Example 22, the WHSV wasabout 0.47 h⁻¹). The results are shown in Table 7 below.

TABLE 7 Results from testing of the catalyst: 13 wt % K₅P₃O₁₀ and 87 wt% fused silica Water Reaction Nitrogen Partial T Pressure, Pressure,AAY, LAC, AAS, PAS, [° C.] [psi] [psi] [mol %] [mol %] [mol %] [mol %]350 360 186.4 25.7 100 25.7 2.57 160 86.9 39.8 100 39.8 2.52 375 360186.4 32.5 100 32.5 2.67 160 86.9 58.6 100 58.6 3.08 80 47 56.4 100 56.43.32 40 27.1 53.8 89.9 59.8 2.59 400 360 186.4 32.5 100 32.5 8.23

Example 23 (Comparative)—26 wt % K₂P₄O₁₁ and 74 wt % Fused SilicaCatalyst

Dipotassium phosphate (K₂HPO₄, 100 wt %, 15.00 g; Fluka, St. Louis, Mo.,catalog #60347), ammonium phosphate dibasic ((NH₄)₂HPO₄, 97.7 wt %,34.92 g; Aldrich, St. Louis, Mo., catalog #379980), and amorphoussilicon oxide (SiO₂, 92.67 g; Aldrich, St. Louis, Mo., catalog #342831)were combined and ground together for 15 min at 500 rpm using aplanetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0227), and 25 grinding balls (Retsch, Haan, Germany, catalog#05.368.0093) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached roomtemperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany; catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (61.0 g).The material was analyzed by XRD and an unknown phase, presumablyK₂P₄O₁₁, was identified as a component of the dehydration catalystprecursor mixture.

Example 24 (Comparative)

1.6 g o the catalyst prepared in Example 23 were mixed with 1.6 g offused silica (Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831;ground and sieved to 102-212 μm) to form a 13 wt % K₂P₄O₁₁ and 87 wt %fused silica catalyst and tested in the experimental setup of and usingthe same procedure as in Example 13 (in this Example 24, the OD of thereactor tube was 1.3 cm (½ in.)). The results are shown in Table 8below.

TABLE 8 Results from testing of the catalyst: 13 wt % K₂P₄O₁₁ and 87 wt% fused silica Water Reaction Nitrogen Partial T, Pressure, Pressure,AAY, LAC, AAS, PAS, [° C.] [psi] [psi] [mol %] [mol %] [mol %] [mol %]250 360 186.4 0.7 9.5 7.6 0 80 47 1.5 36.3 4.1 0 300 80 47 7.3 91.6 8 0375 360 186.4 5.8 100 5.8 0 160 86.9 13.1 100 13.1 0 80 47 17.4 100 17.40

Example 25 (Comparative)—26 wt % K₄P₂O₇ and 74 wt % Fused SilicaCatalyst

Dipotassium phosphate (K₂HPO₄, 100 wt %, 30.00 g; Fluka, St. Louis, Mo.,catalog #60347) and amorphous silicon oxide (SiO₂, 80.97 g; Aldrich, St.Louis, Mo., catalog #342831) were combined and ground together for 15min at 500 rpm using a planetary ball mill PM 100 (Retsch, Haan,Germany; catalog #20.540.0003), a 500 mL grinding jar (Retsch, Haan,Germany; catalog #01.462.0227), and 25 grinding balls (Retsch, Haan,Germany, catalog #05.368.0093) to obtain a fine solid. The solid wastransferred to a 600 mL glass beaker and calcined at 450° C. for 12 hwith a heating ramp of 2° C./min and using a Nabertherm furnace N30/85HA with P300 controller (Nabertherm, Lilienthal, Germany, catalog #N30/85 HA). After calcination, the material was kept inside the ovenuntil it reached room temperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany; catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (7.9 g).The material was analyzed by XRD and K₄P₂O₇ was identified as acomponent of the dehydration catalyst precursor mixture.

Example 26 (Comparative)

1.2 g of the catalyst prepared in Example 25 were mixed with 1.2 g offused silica (Sigma-Aldrich Co., St. Louis, Mo.; catalog #: 342831;ground and sieved to 102-212 μm) to form a—13 wt % K₄P₂O₇ and 87 wt %fused silica catalyst and tested in the experimental setup of and usingthe same procedure as in Example 13 (in this Example 26, the OD of thereactor tube was 1.3 cm (½ in.)). The results are shown in Table 9below.

TABLE 9 Results from testing of the catalyst: 13 wt % K₄P₂O₇ and 87 wt %fused silica Water Reaction Nitrogen Partial T, Pressure, Pressure, AAY,LAC, AAS, PAS, [° C.] [psi] [psi] [mol %] [mol %] [mol %] [mol %] 250360 186.4 1.2 14.5 8.3 0 80 47 2.8 41.1 6.8 0 300 80 47 20.9 88.3 23.7 0350 160 86.9 28.9 92 31.4 1 80 47 27.6 85.9 32.1 1.04 375 360 186.4 30.1100 30.1 1.32 160 86.9 35.6 94 37.9 1.36

Table 10 below shows selective results from Tables 7, 8, and 9; andExamples 8 and 14 to compare the effect of the molar ratio of K and P inthe catalyst K_(x)P_(y)O_(z) on the performance.

TABLE 10 Results from catalysts K_(x)P_(y)O_(z) at 375° C. and variouspressures. Catalyst; Water Molar Nitrogen Partial Ratio of Pressure,Pressure, AAY, LAC, AAS, PAS, K and P [psi] [psi] [mol %] [mol %] [mol%] [mol %] Example not according to the present invention K₂P₄O₁₁; 360186.4 5.8 100 5.8 0 0.5 160 86.9 13.1 100 13.1 0 Examples according tothe present invention (KPO₃)_(n); 360 186.4 84.7 100 84.7 N/A 1 160 86.985.8 100 85.8 N/A K₅P₃O₁₀; 360 186.4 32.5 100 32.5 2.67 1.67 160 86.958.6 100 58.6 3.08 Example not according to the present inventionK₄P₂O₇; 360 186.4 30.1 100 30.1 1.32 2 160 86.9 35.6 94 37.9 1.36

Example 27

2.4 g of the catalyst prepared in Example 8 were tested in theexperimental setup of and using the same procedure as in Example 13. Inthis Example the dehydration zone was 22.9 cm (9 in.) long, theevaporator zone was 30.5 cm (12 in.) long and was packed with 5 g offused silica ground to 425 to 600 μm, the GHSV was 4450 h⁻¹, the WHSVwas 0.58 h⁻¹, and the TOS was about 213 h. At TOS of 21.6 h, the overallacrylic acid yield was 81.7 mol %, lactic acid conversion was 93.3 mol%, acrylic acid selectivity was 87.6 mol %, and propanoic acidselectivity was 0.2 mol %.

Example 28 (Comparative)—26 wt % (KPO₃)_(n) and 74 wt % Alumina Catalyst

Dipotassium phosphate (K₂HPO₄, 100 wt %, 20.00 g, 114.8 mmol; Fluka, St.Louis, Mo., catalog #60347), ammonium phosphate dibasic ((NH₄)₂HPO₄,97.7 wt %, 15.52 g, 114.8 mmol; Aldrich, St. Louis, Mo., catalog#379980), and aluminum oxide (Al₂O₃, 77.17 g; Alfa, Ward Hill, Mass.,catalog #43833) were combined and ground together for 15 min at 500 rpmusing a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 500 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0227), and 25 grinding balls (Retsch, Haan, Germany, catalog#05.368.0093) to obtain a fine solid. The solid was transferred to a 600mL glass beaker and calcined at 450° C. for 12 h with a heating ramp of2° C./min and using a Nabertherm furnace N30/85 HA with P300 controller(Nabertherm, Lilienthal, Germany, catalog # N30/85 HA). Aftercalcination, the material was kept inside the oven until it reached roomtemperature.

The calcined solid was ground gently using a mortar and pestle to obtainparticles of less than about 1 cm, followed by grinding for 30 s at 300rpm using a planetary ball mill PM 100 (Retsch, Haan, Germany; catalog#20.540.0003), a 125 mL grinding jar (Retsch, Haan, Germany; catalog#01.462.0136), and 3 grinding balls (Retsch, Haan, Germany; catalog#05.368.0028). Then, the solids were sieved for 5 min using a vibratorysieve shaker AS 200 control (Retsch, Haan, Germany; catalog#30.018.0001), and sieves No. 70 and 140 (USA standard testing sieve,ASTM E-11 specifications; Gilson Company, Lewis Center, Ohio). Theprocess of grinding particles retained on sieve No. 70 followed bysieving was repeated until all the material passed sieve No. 70.Finally, the solid retained on sieve No. 140 was re-sieved for 30 min toobtain a catalyst with particle size between 106 μm and 212 μm (34.9 g).The material was analyzed by XRD and K₃Al₂(PO₄)₃ and T-(KPO₃)_(n), wereidentified as components of the dehydration catalyst precursor mixture.

Example 29 (Comparative)

3.46 g of the catalyst prepared in Example 28 were tested in theexperimental setup of and using the same procedure as in Example 13. Inthis Example the bottom zone was 6.4 cm (2.5 in.) long, the GHSV was4422 h⁻¹, the WHSV was 0.32 h⁻¹, and the TOS was 5.7 h. The overallacrylic acid yield was 11.3 mol %, lactic acid conversion was 53.5 mol%, acrylic acid selectivity was 21.2 mol %, and propanoic acidselectivity was 5.05 mol %.

The foregoing description is given for clearness of understanding only,and no unnecessary limitations should be understood therefrom, asmodifications within the scope of the invention may be apparent to thosehaving ordinary skill in the art.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, comprising any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A method of making acrylic acid, acrylic acidderivatives, or mixtures thereof comprising contacting the followingcompositions under conditions including a water partial pressure and atemperature: a) hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof; b) water vapor; and c) a dehydrationcatalyst consisting essentially of one or more amorphous phosphatesalts; wherein said one or more amorphous phosphate salts consistessentially of: i) one or more monovalent cations selected from thegroup consisting of K⁺, Rb⁺, Cs⁺, and mixtures thereof, and ii) one ormore phosphate anions selected from the group represented by empiricalformula (I):[H_(2(1−x))PO_((4−x))]⁻  (I); wherein x is any real number equal to orgreater than 0 and equal to or less than 1; wherein said one or moreamorphous phosphate salts in said dehydration catalyst are neutrallycharged; and whereby said acrylic acid, acrylic acid derivatives, ormixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst.
 2. The method ofclaim 1, wherein said hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof are in the gas phase, at leastpartially, during said contacting step with said dehydration catalyst.3. The method of claim 1 wherein the water partial pressure during saidcontacting step in said gas mixture is equal to or greater than about0.8 bar.
 4. The method of claim 1 wherein the water partial pressureduring said contacting step in said gas mixture is equal to or greaterthan about 4 bar.
 5. The method of claim 1 wherein said contacting stepis performed at a temperature equal to or greater than about 250° C. 6.The method of claim 1, wherein at least one of said one or moreamorphous phosphate salts consists of two or more different monovalentcations selected from the group consisting of K⁺, Rb⁺, and Cs⁺.
 7. Themethod of claim 1, wherein said dehydration catalyst consistsessentially of one or more amorphous phosphate salts represented byempirical formula (Ia):M^(I)H_(2(1−x))PO_((4−x))  (Ia); wherein M^(I) is a monovalent cation;wherein x is any real number equal to or greater than 0 and equal to orless than
 1. 8. The method of claim 7, wherein said one or moreamorphous phosphate salts are selected from the group consisting of,KH2(1−X)PO(4−X), RbH2(1−X)PO(4−X), CsH2(1−x)Po(4−x), any of theirhydrated forms, and mixtures thereof; wherein x is any real number equalto or greater than 0 and equal to or less than
 1. 9. The method of claim7, wherein said one or more amorphous phosphate salts isKH_(2(1−x))PO_((4−x)); wherein x is any real number equal to or greaterthan 0 and equal to or less than
 1. 10. The method of claim 1, whereinsaid dehydration catalyst consists essentially of one or more amorphousphosphate salts represented by empirical formula (Ib):M_(w) ^(I)N_((1−w)) ^(I)H_(2(1−x))PO_((4−x))  (Ib); wherein M^(I) andN^(I) are essentially two different monovalent cations; wherein x is anyreal number equal to or greater than 0 and equal to or less than 1;wherein w is any real number greater than 0 and less than
 1. 11. Themethod of claim 10, wherein said one or more amorphous phosphate saltsare selected from the group consisting ofK_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrated forms, andmixtures thereof; wherein x is any real number equal to or greater than0 and equal to or less than 1; wherein w is any real number greater than0 and less than
 1. 12. The method of claim 1, wherein said dehydrationcatalyst further consists of silicon oxide (SiO₂) and wherein saidsilicon oxide is substantially chemically inert to said one or moreamorphous phosphate salts.
 13. The method of claim 12, wherein theweight ratio between the total amount of said one or more amorphousphosphate salts and the total amount of said silicon oxide in saiddehydration catalyst is between about 1:10 and about 4:1.
 14. The methodof claim 12, wherein said silicon oxide is selected from the groupconsisting of amorphous silica, quartz, tridymite, cristobalite,moganite, coesite, and mixtures thereof.
 15. The method of claim 14,wherein said one or more amorphous phosphate salts are selected from thegroup consisting of KH_(2(1−x))PO_((4−x)), RbH_(2(1−x))PO_((4−x)),CsH_(2(1−x))PO_((4−x)), any of their hydrated forms, and mixturesthereof; wherein x is any real number equal to or greater than 0 andequal to or less than 1; and wherein said silicon oxide is selected fromthe group consisting of amorphous silica, quartz, and mixtures thereof.16. The method of claim 15, wherein said one or more amorphous phosphatesalts is KH_(2(1−x))PO_((4−x)); wherein x is any real number equal to orgreater than 0 and equal to or less than 1; and wherein said siliconoxide is amorphous silica.
 17. The method of claim 1, wherein saiddehydration catalyst further consists of one or more oxysaltscomprising: one or more polyvalent cations, and one or more oxyanionsselected from the group represented by molecular formulae (II) and(III):[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−)  (II)[Ta_(2d)O_((5d+e))]^(2e−)  (III); wherein a and b are positive integersor zero; wherein c, d, and e are positive integers; wherein (a−2b) isequal to or greater than zero; wherein (2c−a) is greater than zero;wherein said one or more oxysalts are neutrally charged; and whereinsaid one or more oxysalts are substantially chemically inert to said oneor more amorphous phosphate salts.
 18. The method of claim 17, whereinthe weight ratio between the total amount of said one or more amorphousphosphate salts and the total amount of said one or more oxysalts insaid dehydration catalyst is between about 1:10 and about 4:1.
 19. Themethod of claim 17, wherein said one or more oxyanions are selected fromthe group represented by molecular formulae (IIa) to (IId), (IIIa) to(IIIg), and mixtures thereof:[SO₄]²⁻  (IIa)[S₂O₇]²⁻  (IIb)[HSO₄]¹⁻  (IIc)[SO₄]²⁻.[HSO₄]⁻  (IId)[Ta₂O₆]²⁻  (IIIa)[Ta₂O₇]⁴⁻  (IIIb)[Ta₂O₉]⁸⁻  (IIIc)[Ta₂O₁₀]¹⁰⁻  (IIId)[Ta₂O₁₁]¹²⁻  (IIIe)[Ta₄O₁₁]²⁻  (IIIf)[Ta₄O₁₅]¹⁰⁻  (IIIg).
 20. The method of claim 17, wherein said one ormore oxyanions are selected from the group represented by molecularformulae (IIa), (IIIa), and mixtures thereof:[SO₄]²⁻  (IIa)[Ta₂O₆]²⁻  (IIIa).
 21. The method of claim 17, wherein said one or moreoxysalts are selected from the group consisting of CaSO₄, SrSO₄, BaSO₄,SrK₂(SO₄)₂, SrRb₂(SO₄)₂, Ca₂K₂(SO₄)₃, Ca₂Rb₂(SO₄)₃, Ca₂Cs₂(SO₄)₃,CaTa₄O₁₁, SrTa₄O₁₁, BaTa₄O₁₁, MgTa₂O₆, CaTa₂O₆, SrTa₂O₆, BaTa₂O₆,Mg₂Ta₂O₇, Ca₂Ta₂O₇, Sr₂Ta₂O₇, SrK₂Ta₂O₇, Ba₂Ta₂O₇, Ba₃Ta₂O₈, Mg₄Ta₂O₉,Ca₄Ta₂O₉, Sr₄Ta₂O₉, Ba₄Ta₂O₉, Ca₅Ta₂O₁₀, Ca₂KTa₃O₁₀, Ca₂RbTa₃O₁₀,Ca₂CsTa₃O₁₀, Sr₂KTa₃O₁₀, Sr₂RbTa₃O₁₀, Sr₂CsTa₃O₁₀, Mg₅Ta₄O₁₅, Sr₅Ta₄O₁₅,Ba₅Ta₄O₁₅, Sr₂KTa₅O₁₅, Ba₂KTa₅O₁₅, Sr₆Ta₂O₁₁, Ba₆Ta₂O₁₁, any of theirhydrated forms, and mixtures thereof.
 22. The method of claim 21,wherein said one or more oxysalts are selected from the group consistingof CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any of their hydratedforms, and mixtures thereof.
 23. The method of claim 17, wherein saidone or more amorphous phosphate salts are selected from the groupconsisting of KH_(2(1−x))PO_((4−x)), RbH_(2(1−x))PO_((4−x)),CsH_(2(1−x))PO_((4−x)), any of their hydrated forms, and mixturesthereof; wherein x is any real number equal to or greater than 0 andequal to or less than 1; and wherein said one or more non-phosphatecompounds are selected from the group consisting of CaSO₄, CaTa₂O₆,SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any of their hydrated forms, andmixtures thereof.
 24. The method of claim 23, wherein said one or moreamorphous phosphate salts is KH_(2(1−x))PO_((4−x)); wherein x is anyreal number equal to or greater than 0 and equal to or less than 1; andwherein said one or more non-phosphate compounds is BaSO₄.
 25. Themethod of claim 1, wherein said hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof are lactic acid, lactic acidderivatives, or mixtures thereof.
 26. The method of claim 2, whereinsaid hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof and water vapor are a gas mixture.
 27. The method ofclaim 26, wherein said gas mixture further comprises an essentiallychemically inert gas selected from the group consisting of nitrogen,helium, argon, carbon dioxide, carbon monoxide, air, water vapor, andmixtures thereof.
 28. The method of claim 3, wherein said temperature isbetween about 300° C. and about 450° C.
 29. The method of claim 1,wherein said contacting step with said dehydration catalyst is performedunder a total pressure of at least 1 bar.
 30. The method of claim 29,wherein said total pressure is between about 4 bar and about 35 bar. 31.A method of making acrylic acid, acrylic acid derivatives, or mixturesthereof comprising contacting the following compositions underconditions including a water partial pressure and a temperature: a gasmixture comprising: a) hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof; and b) water vapor; with a dehydrationcatalyst precursor mixture consisting essentially of one or moreprecursor phosphate salts; wherein said one or more precursor phosphatesalts consist essentially of: i) one or more monovalent cations, and ii)one or more phosphate anions selected from the group represented bymolecular formulae (IV) and (V):[H₂P_(y)O_((3y+1))]^(y−)  (IV)[PO₃]_(z) ^(z−)  (V); wherein y is any integer number equal to orgreater than 1; wherein z is any integer number equal to or greater than3; wherein said one or more precursor phosphate salts are neutrallycharged; wherein the water partial pressure during said contacting stepin said gas mixture is equal to or greater than the water partialpressure at the triple point of said one or more precursor phosphatesalts; and whereby said acrylic acid, acrylic acid derivatives, ormixtures thereof is produced as a result of said water vapor and saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof being contacted with said dehydration catalyst precursormixture.